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ROR observatory concrete slab versus wooden deck questions

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#1 Pleiadescgs

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Posted 11 April 2021 - 11:33 AM

Hello,

 

            I am about to have a ROR observatory built by BYO and I am going back and forth in my mind as to concrete slab versus wooden deck floor option. I know that this issue has been discussed frequently here and after reviewing what I could find on this forum as well as other web searches I am still unsure on the best approach or if I am just splitting hairs.

         

            My main goal is for remote astrophotography and it is that consideration which is the primary one in question.  However I also need to plan for the observatory's alternate use which will be for visual observers when I'm not using it and also when I'm too old to do to anymore.  I have pretty much decided that I will isolate the telescope piers regardless of whether it is a slab or deck floor although one could make the argument that that doesn't really matter if I am doing just all remote.  So my main concern is the thermal issues with concrete.  Although the slab will be covered all day by the roof, the interior temp can get very warm in summertime.  I understand the slab may stay cool because it's in the ground but if its warm enough inside wouldn't there be some heat transfer to the concrete even though heat rises and then be some slow dissipation at night.

            BYO has options for air conditioner cutouts and roof vents ( I will probably definitely add the vents) plus the roof is metal not asphalt shingles. So I assume some folks do use air conditioners and other climate control measures. I also saw where some folks put roof radiant barrier insulation in as well and where some insulate the entire structure.  Also seeing that there are remote observatories that use concrete slabs out west one would assume that it is really not that big of an issue but maybe they have interior climate control

 

             I know I could just go with the wooden deck and be done with it but the concrete floor does have some advantages that scopes could be setup on tripods for visual or moved around easier in the future.  Also I will have a large (18") DOB that will be all set up in there but stored to be wheeled outside for visual observing in addition to the astrophotography piers .  In order to use all of those in the observatory I would need to spend a lot more money for a larger structure, additional DOB pad, and reduced open wall height but I am not considering any of that.

 

             So my question is....... Do most of you with ROR observatories with concrete slabs that you use for astrophotography have internal climate control to handle any thermal issues with  using insulation, air conditioners etc. or is it really not that big of an issue as long as you open the roof for a couple of hours prior to using?  Do you see any negative effects with your images that you can correlate with thermal currents from the concrete floor.  Or as I said earlier am I just splitting hairs.  I will probably be using mostly narrowband imaging because my area has heavy light pollution and marginal seeing most of the time. I would rather not add thermal issues to the mix.

 

Thanks for any feedback you can give.  Chris

 

 



#2 astrokeith

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Posted 11 April 2021 - 11:46 AM

I'd go for the concrete slab, for stability and longevity.

 

I dont have such a severe climate, but for other reasons I covered my floor with cushion 'rubber' interlocking floor tiles. They are about 1cm thick and remarkable comfortable to stan don for a while and they have saved more than one accidentally dropped item.

 

The tiles would help keep the slab at ground temperature during the day, and at night slow up the emission of heat from the slab.


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#3 petert913

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Posted 11 April 2021 - 11:50 AM

Wood is okay....as long as the pier or tripod are isolated from it.  Otherwise - Slab all the way.


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#4 ac4lt

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Posted 11 April 2021 - 11:53 AM

I'm in a similar situation. My understanding is the slab floor will retain more heat so the wood floor will equilibrate more quickly. If you need to bring in a new cable under the floor in the future and your wood floor is raised up a bit then it's easier to make those kinds of changes in the future though I suppose you could plan for that by having some extra conduit in place when you pour the slab.

 

I'm planning on wood but will be following this thread with interest.


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#5 Supernova74

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Posted 11 April 2021 - 11:57 AM

Well unfortunately regarding all the gizmos and the electronics side of things im sure other forum members can help you there who own similar kind of arrangement!?regarding the build itself I would always rate a concrete base over wood for several reasons,and concrete keeps rather cool anyway during the day time as obviously it’s go to be covered over most of the time,and concrete doesn’t rot like wood can especially when it’s a ground level and of course most probably talking bare minimal hear it would also improve unwanted vibrations for something like a tripod.however if you decided to use decking etc I would definitely make sure the wood is well preserved and have some kind of membrane underneath the main construction to save any damp much as possible.and the noggings in between the the main beams for the floor usually are roughly 1ft 6”apart for exsample would suffice if you was going to construct a decking for something like a patio area so I would put them closer together slightly not only for extra support also for hopefully less vibration.



#6 stargzr66207

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Posted 11 April 2021 - 03:35 PM

For my ROR observatory, I went with a raised wood deck for the floor. It is supported by 12 concrete piers, with a 5/8"-11 threaded bar in each, to which the stud mounts for the floor beams are attached. Details can be seen under the "construction" page of my website which appears in my signature. My observatory has been in operation since early 2003, and I have had no issues with the floor. Still solid as can be! The telescope pier is mounted to a concrete base which extends 4 feet below grade and contains sixteen 80lb bags of concrete. The hole for this pier was hand dug in the site, which is a pasture that has never been tilled. The pier hasn't moved an iota in the past 17 plus years (according to the bubble level on my mount). I went with the wood flooring to assure quick thermal equilibrium. Just my 2-cents!

 

Ron Abbott


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#7 Pleiadescgs

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Posted 11 April 2021 - 07:21 PM

Thank you all for your responses so far.  I really appreciate it.

 

            Astrokeith suggestion about rubber tiles sound like a nice idea for the concrete slab insulation and worth pursuing.  I know exactly the things you are talking about.

            I do realize all things considered that a wood floor would be best for the thermal issues if that was my only concern but concrete would be more stable and long lasting plus give me more flexibility with using tripods etc as supernova states.  Peter, do you do astrophotography? as I take it you have a concrete floor? You didn't say.

           It seems there are many people that mention the thermal equilibrium suggestion in deciding their floor option and why they don't choose concrete. Others say there is no real issue with concrete since its covered all day.  So I guess I'm just trying to justify that I will have no big thermal problems with a concrete slab floor since my primary goal is astrophotography  and I want to feel good about my decision.  Scott at BYO didn't think there was an issue. I may just have to pick one option and hope for the best. But I was just wondering if there were some out there that have concrete floors in ROR designs and are doing astrophotography and wished they would have gone with wood floor instead. That would be helpful to know.  Or if some went with concrete and have no issues because they are doing some sort of climate control inside their observatory (which would probably be a good idea to do anyway for the instruments inside)

           Linda, I do agree that having a wood floor would make it easier in the future to run electric / computer lines underneath and is one of the reasons I am going back and forth on this. Then I don't have have to have that  figured out ahead which would give me time to get everything organized first and see how it all fits. Otherwise I need to run conduit under the slab.  Of course I could do over the floor runs covered with pads or tape but would rather stay away from that option.

           It is neat seeing all the different options and designs everyone is doing like yours Peter  with their observatories and I suspect there are many ways to do everything.  I'm not a spring chicken anymore so once mine is done I can't do it over again. Thanks, Chris



#8 syxbach

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Posted 11 April 2021 - 09:31 PM

Chris

 

Check out observatory. Just built by BYO. Go concrete, no regrets!

 

Yuexiao
 

https://www.cloudyni...bservatory-wto/

 

Hello,

 

            I am about to have a ROR observatory built by BYO and I am going back and forth in my mind as to concrete slab versus wooden deck floor option. I know that this issue has been discussed frequently here and after reviewing what I could find on this forum as well as other web searches I am still unsure on the best approach or if I am just splitting hairs.

         

            My main goal is for remote astrophotography and it is that consideration which is the primary one in question.  However I also need to plan for the observatory's alternate use which will be for visual observers when I'm not using it and also when I'm too old to do to anymore.  I have pretty much decided that I will isolate the telescope piers regardless of whether it is a slab or deck floor although one could make the argument that that doesn't really matter if I am doing just all remote.  So my main concern is the thermal issues with concrete.  Although the slab will be covered all day by the roof, the interior temp can get very warm in summertime.  I understand the slab may stay cool because it's in the ground but if its warm enough inside wouldn't there be some heat transfer to the concrete even though heat rises and then be some slow dissipation at night.

            BYO has options for air conditioner cutouts and roof vents ( I will probably definitely add the vents) plus the roof is metal not asphalt shingles. So I assume some folks do use air conditioners and other climate control measures. I also saw where some folks put roof radiant barrier insulation in as well and where some insulate the entire structure.  Also seeing that there are remote observatories that use concrete slabs out west one would assume that it is really not that big of an issue but maybe they have interior climate control

 

             I know I could just go with the wooden deck and be done with it but the concrete floor does have some advantages that scopes could be setup on tripods for visual or moved around easier in the future.  Also I will have a large (18") DOB that will be all set up in there but stored to be wheeled outside for visual observing in addition to the astrophotography piers .  In order to use all of those in the observatory I would need to spend a lot more money for a larger structure, additional DOB pad, and reduced open wall height but I am not considering any of that.

 

             So my question is....... Do most of you with ROR observatories with concrete slabs that you use for astrophotography have internal climate control to handle any thermal issues with  using insulation, air conditioners etc. or is it really not that big of an issue as long as you open the roof for a couple of hours prior to using?  Do you see any negative effects with your images that you can correlate with thermal currents from the concrete floor.  Or as I said earlier am I just splitting hairs.  I will probably be using mostly narrowband imaging because my area has heavy light pollution and marginal seeing most of the time. I would rather not add thermal issues to the mix.

 

Thanks for any feedback you can give.  Chris

 



#9 Pleiadescgs

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Posted 12 April 2021 - 09:30 AM

Yuexaio,

 

Thanks for sharing your project that Scott just did.  So since you are doing remote I assume astrophotography is your main purpose. Are you planning on doing any temperature control inside the observatory or you don't think that's an issue?  Any concerns you have with the thermal currents from the concrete or you are not concerned?  I see you have no windows which is good.  I am planning BYO 11.5 x 15.5 structure with two piers although I might change it to your size since I will be storing a large 18 inch Dob in there to to be rolled out for use as well but otherwise mostly remote.  It was good seeing your pier distance with the 5 ft separations.  I was thinking 6ft but after seeing yours it looks like 5 ft. would be good enough. I also have Ap1100 mount with a TEC 140 which would be my biggest.  I see you did a 6 inch slab. My builder was going to do a 4 inch slab but with expanded footers around the perimeter.  I am in Pa.    Chris



#10 CarolG

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Posted 12 April 2021 - 09:51 AM

I have had two observatories.  The first one was a domed observatory built on a wood deck.  It was very stable and had few thermal issues (was in southern Oklahoma where it gets extremely hot and humid).  The big problem was the animal problem.  Mice came in easily under the deck as well as snakes and burrowing animals.  It was a constant battle keeping them out.  Because of this, my second observatory was on a concrete slab and built by BYO.  I still had the occasional mouse or two, but it was manageable.  This observatory was in central Oklahoma, so it was still hot and humid in the summer.  I did have a warm room and BYO cut out a place to put in a window air conditioner.  It kept the warm room cool and space heaters kept it warm in the winter.  As far as the scope room, rolling back the roof before I observed helped the heat escape and the temperature to stabilize.  Also a couple of windows in the warm room were left open in the heat of the day to allow circulation.  BYO will soon build my third observatory, and it will be on a concrete slab. Linda brought up a good point about cabling, but if you plan ahead and put in conduit large enough, that should not be a problem. On this new build of mine, I will put in larger conduit, because I learned before that wires and cables can fill up a conduit pretty fast.



#11 syxbach

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Posted 12 April 2021 - 10:08 AM

Chris

 

Stability and animal issues are what we concern firstgrin.gif. We have not thought about temperature control. If we add fans or put one outlet, sand, insect or birds may go in. In the future, we will add insulation layers, maybe add a fan with filter if necessary. I went there last week, outside is 80-85 F, inside is pretty cool. What our team will do is to open the roof at least ~1 hour before sunset to let the temperature equilibrate in the future. 

 

Best

 

Yuexiao

 

 

Yuexaio,

 

Thanks for sharing your project that Scott just did.  So since you are doing remote I assume astrophotography is your main purpose. Are you planning on doing any temperature control inside the observatory or you don't think that's an issue?  Any concerns you have with the thermal currents from the concrete or you are not concerned?  I see you have no windows which is good.  I am planning BYO 11.5 x 15.5 structure with two piers although I might change it to your size since I will be storing a large 18 inch Dob in there to to be rolled out for use as well but otherwise mostly remote.  It was good seeing your pier distance with the 5 ft separations.  I was thinking 6ft but after seeing yours it looks like 5 ft. would be good enough. I also have Ap1100 mount with a TEC 140 which would be my biggest.  I see you did a 6 inch slab. My builder was going to do a 4 inch slab but with expanded footers around the perimeter.  I am in Pa.    Chris



#12 Tom K

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Posted 12 April 2021 - 11:25 AM

My vote would be concrete with lots of extra conduit space.   



#13 Supernova74

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Posted 12 April 2021 - 02:00 PM

I,m thinking most of us can agree on this thread there are pros and cons in useing both methods!?like all the Astro-kit we all own there is no such thing as a perfect scope!?and the same philosophy I’m guessing remains the same in some ways in all the observatory’s we all build.im seeing some more initial obstacles regarding the wood based or decking for the base which I also mentioned in one of my previous posts.in laying a membrane material on the floor then having joists across with noggings in between the joists,then assuming this will be raised up approximately around 6” for general air flow circulation and the more obvious reason damp etc to stop the beams rotting.i think some other forum member did mention about using wood or decking myself including however just thinking outside the box moment!?this would allow easier access to cable management if the op decided to route all his cables underneath which also would need watar proof insulation aswell he would have easier access to the cables of any power would fail to the scope or mount.

 

however this would have to be carefully designed and planned if this method was chosen as generally the principle applies 

in all the slats or decking boards fixed down with a nail gun then the outer walls of the framing are then erected on top of the base.i can see this just creating more problems useing this method as how would you access the cables if you physically cannot get to them!?as the overall construction if not careful would be permanently fixed.so either method would be suitable 

with some clever designing however I would still rate the concrete method and just make sure that all cables are easily accessible around 6” or so above the floor inside the observatory itself.not only concrete keeps very cool in summer months also for overall integrity of the structure.and maybe some vibration absorbing potential.

 

i also 100% agree useing rubber based tiles inside the observatory itself as I’ve seen this to become very popular in more home grown observatorys here in the uk.just to add I used to manufacture out houses and backyard sheds which people also used for all various types of applications like home office,gyms,play houses etc the most difficult part would be the roof design and the mechanical side of things,the rest is in most part quite easy to build with 4x2 timber 2x2 and so on and the cladding so to speak use shiplap boards and tounge and groove boards.



#14 Tom K

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Posted 12 April 2021 - 02:44 PM

As I was considering my previous "vote" I realized that I did not know the site conditions.   If you have perfectly flat ground a slab is cheap and easy.  If there is a slope to it the cost of grading a flat spot and retaining the earth on the high side adds considerably to the project.   On a sloped site the wood framed base is likely a more cost effective way to go.



#15 Pleiadescgs

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Posted 13 April 2021 - 07:45 PM

Thanks all.

 

In answer to some questions/comments.  

My site is pretty flat so doing concrete slab would work pretty easily.

 

It is unfortunately not on real high ground so it could tend to have more moisture pockets around and so perhaps the foundation of a wood deck would be more susceptible to future rot issues. 

 

Also where I am putting this structure it will have an alternative use not just for me but for a local nature center into the future so the more stable the structure the better for long term.  So concrete slab is still my preferred at this point.

 

I am certainly in agreement on the pros and cons.   Both systems do work adequately for many and I would probably be fine either way with a slab or wood deck, as many are.  

 

We all know, and physics tells us, that concrete can be a huge heat sink that is slow to dissipate that heat however it seems after reading many stories and comments on this subject it seems that this is really not an issue for most.  Those that do choose concrete slabs for their observatory floors are happy with their choice, have roof on all day, concrete is in contact with the cooling earth, and might possibly do some internal temp control or insulation don't really have the thermal issues.  So I can be good with that.  Since I am a relative newbie to astrophotography, have bad seeing most of the time, very heavy light pollution, I just didn't want to make matters even worse with rising heat currents.  It would seem though that that is the least of my worries.  Thanks all.  



#16 BKBrown

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Posted 14 April 2021 - 11:59 AM

Hi Chris,

 

I am currently facing exactly the same dilemma that you are in getting ready for a visit from BYO. On the plus side, I just got off of the phone with my new cement guy and have decided to go the slab route if he comes in at or below budget. Unfortunately, the site has some slope to it and will require grading and drainage adjustments. But I live in a very rural area and don't want to deal with local critters taking up residence under my observatory, and I want to increase the longevity of the structure by not having to rely on wood support posts set in concrete, so a slab would be my ideal approach. The observation floor will have two steel piers on isolated rebar and cement footers, and they will have electrical cable and fiber at each station connecting them to the warm room. Orientation and tolerances need to be tight so there is still a lot of planning that needs to be done. Good luck!

 

Clear Skies,

Brian snoopy2.gif



#17 HunterofPhotons

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Posted 14 April 2021 - 01:47 PM

..... But I live in a very rural area and don't want to deal with local critters taking up residence under my observatory, and I want to increase the longevity of the structure by not having to rely on wood support posts set in concrete, so a slab would be my ideal approach.....

Clear Skies,

Brian

 

Will the walls of your observatory be standard wood construction?

If so, do you realize that building on a ground level slab will cause the bottom of the wood walls to rot and give easy access to your critters.

 

dan k.



#18 Tom K

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Posted 14 April 2021 - 02:04 PM

Will the walls of your observatory be standard wood construction?

If so, do you realize that building on a ground level slab will cause the bottom of the wood walls to rot and give easy access to your critters.

 

dan k.

I disagree - properly constructed wood frame on slab buildings (pressure treated sill plate, appropriate height of slab above surrounding grade, etc) works just fine in millions of buildings.


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#19 MikiSJ

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Posted 14 April 2021 - 03:29 PM

As a homebuilder with over 4,000 homes under my belt, I would always prefer a raised wood floor, but concrete slab floors are quicker and cheaper to build than a perimeter foundation and wood sub-floor.

 

Today, if I were to build a ROR structure of say 12'x12', I would use a perimeter concrete foundation and a wood sub-floor with a concrete pier for the mount.

 

Anything smaller than say, 12'x12' would likely use a concrete slab simply for economic and ease of construction.


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#20 Tom K

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Posted 14 April 2021 - 04:54 PM

As a homebuilder with over 4,000 homes under my belt, I would always prefer a raised wood floor, but concrete slab floors are quicker and cheaper to build than a perimeter foundation and wood sub-floor.

 

Today, if I were to build a ROR structure of say 12'x12', I would use a perimeter concrete foundation and a wood sub-floor with a concrete pier for the mount.

 

Anything smaller than say, 12'x12' would likely use a concrete slab simply for economic and ease of construction.

The best of both worlds!   On a side note, it has always amazed me that builders of slab homes ran the water lines under the slab.   I manage a water utility and we get LOTS of customers with huge bills they can't figure out until the feel the floor getting warm when the hot water side starts leaking.   Super expensive and disruptive to fix.   Had they run them in the attic and walls it would be a small drywall patch, but a slab leak - egad what a mess.



#21 MikiSJ

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Posted 14 April 2021 - 05:26 PM

An anecdote about water pipes in homes.

 

When I first joined a major homebuilder in California in 1977, my first staff meeting involved all departments including Warranty. The head of the Warranty department mentioned that a homeowner in a recently completed townhouse project in San Jose CA, was sitting by his television when all of a sudden he started to get a spray of water in his ear. This was the start of a very expensive and time consuming problem.

 

At the time of this incident, the water supplier for this project used a specific well located in the vicinity of the project. The plumbing for this project did not use a slab floor but rather a raised foundation.

 

The plumbing sub-contractor purchased all of his copper fittings from one manufacturer. 

 

To make a long story as short as possible, the 90º and 45º copper elbows the plumbing contractor used interacted with an unusual chemical in the local well's water and after a relatively short time (<2 years), the elbows would develop pin holes allowing the house water, under pressure, to leak and if the leak was pointed in the right direction, then the leak might hit someone in the ear with a spray of water.

 

This was a relatively large project with 144 townhouses and we started to get more complaints of water leakage in the walls and ceilings of the units.

 

My builder, which was owned by a major insurance company, elected to replace all of the copper piping in units with copper pipe and copper fittings that were tested against the water supplied to the project. A VERY expensive fix.

 

The lawyers were engaged and the plumbing contractor, the copper fitting supplier and the water supplier were all sued and the result was a lot of angry townhome owners who were returned to normal and a builder who did not have too much of a financial loss.

 

A couple of years ago, I met a new friend who happened to still live in this project and he remember when the plumbing crew came in ripping up drywall and installing all new piping in his home. He laughs about it now, but was really annoyed when it happened.

 

So, the moral of this story is, don't plumb a concrete slab with copper pipe. Sanitary lines using ABS plastic piping and now, PEX piping remove most of the future liability of having plumbing in a slab. Hot water supplied should always be above the slab.



#22 GrandadCast

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Posted 14 April 2021 - 09:23 PM

My descission was easy once a bid for the cement pumper got involved. Long slope with quick drops just does not play well with cement trucks.

 

Jess



#23 Umasscrew39

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Posted 15 April 2021 - 05:09 AM

 "So my question is....... Do most of you with ROR observatories with concrete slabs that you use for astrophotography have internal climate control to handle any thermal issues with  using insulation, air conditioners etc. or is it really not that big of an issue as long as you open the roof for a couple of hours prior to using?  Do you see any negative effects with your images that you can correlate with thermal currents from the concrete floor.  Or as I said earlier am I just splitting hairs.  I will probably be using mostly narrowband imaging because my area has heavy light pollution and marginal seeing most of the time. I would rather not add thermal issues to the mix."

 

 

Chris- 

 

Well- I actually took a little different approach.  I did a concrete slab which I think is most stable if done correctly (both in depth and width) but then had the cement pier run up 10 feet above ground level where I built an observatory room with wooden flooring. At that point, I added an adjustable steel pier on top of the cement pier.  For example, the pier should have a 4:1 ratio, or less, between height and diameter.  When I investigated building mine, I was told to use a tapered, welded, open-framed steel pier over an untapered steel tube or concrete pier as that helps  with thermal inertia.  The room is temperature and humidity controlled with a split AC unit.  With this design, my C11" EdgeHD (notorious for need a long time to equilibrate) needs only minimal time to equilibrate to the outside environment once the ROR is opened.  Minimal time, meaning usually around 30-45 minutes, 1 hr at most.  

 

So, pier design, flooring, and the scope itself all factor into the very good questions you are asking.

 

 

Bruce



#24 HunterofPhotons

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Posted 15 April 2021 - 12:17 PM

I disagree - properly constructed wood frame on slab buildings (pressure treated sill plate, appropriate height of slab above surrounding grade, etc) works just fine in millions of buildings.

 

It's not just the sill plate, it's the siding and the underlying sheathing that can rot.

What is the appropriate height of slab?  In temperate climates with termites we're talking 10-12" minimum above grade by code.  OP is in Pennsylvania.

 

dan k.



#25 stargzr66207

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  • Loc: Kansas, USA

Posted 15 April 2021 - 12:25 PM

To all who have mentioned critters in the preceding posts:  My observatory is in a rural location, in the middle of a hayfield. It has been in operation for 17yrs now. Common field mice have always been a problem. In a rural location like mine, it is impossible to keep mice out, regardless of the type of structure you have! I am amazed at how these little beasts can get in!  I might add that even at my home in a suburban location, well settled since the mid-'60s, I still get an occasional mouse.

In an observatory there are SO many places that they can get in, including the gap between the floor and the pier, as well as anyplace where electrical conduit and piping enter the structure.

By not leaving anything outside of storage cabinets that they might use for nesting material, as well as NEVER leaving any food between visits, I have kept the infestation down to the level of a manageable nuisance (cleaning up mouse droppings left between visits).

BTW, I have tried EVERY kind of animal deterrent advertised (ultrasonic noise, loud audible noise, electromagnetic waves, etc, all to no avail.  Since my observatory floor is raised above ground level, burrowing rodents (groundhogs, gophers, etc.) have not been a problem. The mice, however, are just something you have to live with.

 

Ron Abbott




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