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Observatory wall construction questions.

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#1 George P Dunham

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Posted 23 January 2020 - 10:04 AM

I am building a 10' x 10' observatory.  I'm getting ready for the walls and need direction. 

 

I am in western colorado at 6800 feet.  Winters are cold (lows in the low 30's - 0's) and summers are hot (highs in the upper 80's-90's).  The sun heats the south and west sides of my house strongly and I am concerned that the same will happen inside the observatory.  My goal is to make the walls as thermally neutral as possible within reason.

 

So, the basic construction will use 2x6 framing and standard 1/2" exterior board  with James Hardy siding on the exterior with drywall on the interior.  I will have a vapor barrier in place.  I will have wall vents and an exhaust fan to turn interior air over quickly.  I am thinking a aluminum covered foam insulating board in the the south and west facing walls if not all four walls.  I understand that having no insulation would be good but I want the interior temp to stay cool during the day in the summer but to follow ambient temp in the winter.  I am not planning on an air conditioner for summer use but perhaps that might might be needed.

 

Bottom line, what are my options?

 



#2 Terry White

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Posted 23 January 2020 - 10:46 AM

The highest R-value rigid foam board you can buy is Johns Manville AP™ Foil-Faced Polyiso Foam Sheathing: https://www.jm.com/e...rd---sheathing/ I used 3" thick sections on the walls and floor in my 10' x 10' observatory and it has performed quite admirably.


Edited by Terry White, 23 January 2020 - 10:52 AM.


#3 han.k

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Posted 23 January 2020 - 11:28 AM

You need constant ventilation to get rid of moisture. Without ventilation moisture will condense on your equipment during the night due to cooling. Having ventilation, insulation doesn't make sense. You better invest in Sun shielding like a zinc coated reflective roof to reflect the Sun radiation during the day. Also in wall materials which cool down quickly in the evening like wood. Metal part will attract moisture, wood much less.

 

In hot summer, my shed (zinc coated roof , wooden walls) doesn't get more then 5 or 6 degrees Fahrenheit hotter then the environment and is full of vent holes.

 

Han


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#4 nmoushon

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Posted 23 January 2020 - 11:46 AM

I think you are miss understanding how insulation works in a building envelope. Putting it on one or two walls but no where else will do nothing to help control the temperature inside. If you are going to put in any insulation at all you might was well do the whole thing...walls and roof. BUT if you are not wanting to put A/C or heat then insulation will actually make things worse. Because now you have created a moisture & temperature trap. So I advise against adding any insulation at all....unless you are trying to create a warm room to the side but thats different and it doesnt sound like you are. The air circulation is actually what will do the most benefit. Since you are trying to achieve ambient air temps the air circulation is what if doing the work for you, not the insulation. Hook up a couple powered roof vents along with plenty of cross vents and low vents and you will have no problem keeping the obsy within a couple degrees of ambient. Now what you will have figure out for your specific location is where the prevailing winds are coming from. This is key if you really want to control the temp. The cross vents (non-powered ones) become very less efficient if they are not directed at the prevailing wind direction. So it could be beneficial to orient your building other than on a North-South axis, which is typical. I'm not saying if you dont orient the build for the winds the vents are useless, just that you should consider it. 

 

Your temperature ranges you mentioned actually arent that bad. Plenty of locations that have much more temperature swings in the seasons and most of those do not have insulation. My location for example gets just as cold as yours but we get up to 110 F in the summers. All the obsy I know of in my area dont have insulation. 

 

If you are really concerned about the southern exposure I would suggest finding ways to create shade or pick certain exterior materials to help reflect the heat away instead of absorbing it. Light paint colors (doesnt have to be white) help a lot. Dont use black asphalt shingles. Plant some medium size shrubs/trees near the south wall so that they create shade. Just keep the trimmed so they dont block any views. But keep in mind trees and shrubs block wind as well. So if your prevailing winds come from the south you wouldnt want to do this. 


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#5 bobzeq25

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Posted 23 January 2020 - 11:58 AM

You need constant ventilation to get rid of moisture. Without ventilation moisture will condense on your equipment during the night due to cooling. Having ventilation, insulation doesn't make sense. You better invest in Sun shielding like a zinc coated reflective roof to reflect the Sun radiation during the day. Also in wall materials which cool down quickly in the evening like wood. Metal part will attract moisture, wood much less.

 

In hot summer, my shed (zinc coated roof , wooden walls) doesn't get more then 5 or 6 degrees Fahrenheit hotter then the environment and is full of vent holes.

 

Han

+1.  And the vapor barrier is a particularly bad idea, especially in a dry climate.  You _want_ moisture to be able to move back and forth.The key to this all is ventilation.

 

My house has the west sun problem, big time.  Brick siding retains and reradiates daytime heat, for hours.  My wife doesn't understand why we need to run the air con well into the cool night.

 

My observatory walls are a plastic garden shed, reinforced by a conventional 2X4 frame.  The aluminum flat panel roof has a full length high quality ridge vent at the top.  There's some insulation between it and the observatory.  The area behind the eaves is deliberately left completely open.  Thermal heating pulls air out the roof vent, in through the eaves.  The observatory stays quite close to the air temperature (you can do little better), the roof reflects the sun, protects the equipment from it.  I open it fully at dusk.   I never have to use a dew heater.  The equipment got more dew on it when I was using it outside.

 

Watch out for cross venting.  It's all too easy to have air flowing horizontally between them, leaving the area below the roof itself a dead zone.  Especially if you power something.  Previous owner of house made that mistake, managed to get mold in the attic in a dry climate.  I vastly improved the minimal high roof vents, and added missing eaves vents.  Closed off the big horizontal vent with motor, which was pulling a vacuum in the attic drawing in humid air in from the house.  A recent reroof let me replace all the high roof vents with a _lot_ of ridge venting.

 

Air wants to do the right thing.  You just have to guide it properly.  Shoving it around, or impeding its flow, _often_ causes more problem than it solves.   Powered roof vents feel good and make somebody money, using thermal energy properly is better.  You have to insulate a house, to save energy, since you don't want it at outside air temperature.  If an observatory is at outside air temperature, that's pretty good.  I'm close.


Edited by bobzeq25, 23 January 2020 - 12:17 PM.


#6 macdonjh

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Posted 23 January 2020 - 01:30 PM

I agree with the choice of Hardi-plank siding.  Easy to work with (get a nail gun, though, don't even ask me how many nails I bent trying to drive them with a hammer). 

 

My observatory is absolutely not sealed.  I have a large gaps where the roll-off roof meets the fixed walls.  Sure, the siding and trim cover these gaps cosmetically, but do not seal them from air flow.  Wind blows through my observatory.  In addition, I have a vent fan (I think 200 CFM) which is on a thermostat control.  It comes on when it gets hot to keep the inside of the building close to ambient.  I do keep a standard TeleGizmos cover (not the 365 cover) over my scope and mount, but that's mostly for dust.  I don't have any trouble with condensation, it's always dry inside when I go out.

   Ventillation?  Check

 

Inside the walls and the roof I have some 1/2" polyisocyanurate foam insulation boards with a radiant barrier on one side.  I got those for free from a friend who had a bunch left over from building his family's house.  I installed them for the radiant barrier for the same reason George P Dunham is considering insulating his south and west walls: to limit solar gain.  It works.  

   Insulation?  No check

   Radiant barrier?  Check

 

All this advice should be avoided, though, if George P Dunham is considering a warm room for his observatory.  In that case, insulation is desired to keep the heat in the warm room away from his scope and to keep power usage for heat and/ or A/C down.  



#7 George P Dunham

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Posted 23 January 2020 - 02:18 PM

I will have an 8' dome on top of a 10' x 10' room.  No control room.  It will be used semi-remotely 95% of the time so physical comfort is of minor concern. 

 

I am in a very dry area.  Summer monsoon moisture brings us to 35% rh on rare occasions.  We are typically at or less than 15% rh.  I will try to achieve some "sealing" but primarily as a critter barrier.  Vapor barrier will be discussed.  The dome provides free flow of air in and out but has a "brush" surround for dust and critters.  The fan will move 600cfm out of building.  There will be two filtered 16"x8" intake vents on the east and west walls about 2' off the ground.  So ideally I will turn on the fan and open the dome before sunset (will need to fine tune that).  Scope fans will be turned on when interior temp is less than outside temp (will need to fine tune that as well).  I also have a good fan to circulate air inside.

 

Radiant barrier is what I'm looking for.  John Manville AP foil faced sheathing sounds like it's a good option.  The reason is all about radiant heat prevention.  Perhaps more filtered vents would be prudent.   Yes..insulation is not what is needed. 

 

I have a dirt road that is about 1000feet from the observatory and is not too busy ~1 vehicle per hour during the day.  Enough dust is kicked up where filtering any air coming in will be a good idea.   I also have lot's of spiders,wasps and bees around.  So screens will be necessary at all intake points.

 

Good food for thought here...thanks



#8 Chucke

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Posted 23 January 2020 - 02:53 PM

I put radiant barrier in my walls.  Nothing on the ceiling yet.  Roof is white coated steel.  I painted the building white.  I put a brush "seal" on the south end of my ROR to minimize wind  from blowing in dust.  Before the brush I could feel air movement during a good wind.  The remainder of the roof is unsealed and just as BYO built it with no additional ventilation screens or such.  The building is on a concrete slab.  During the daytime, even during summer in AZ, it stays 10F degrees or more cooler inside than ambient.  Right now it is 61F outside and 50F inside.  I have indoor/outdoor temperature sensors and don't open the roof until the outside temperature matches the inside.


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#9 nmoushon

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Posted 23 January 2020 - 04:06 PM

I will have an 8' dome on top of a 10' x 10' room.  No control room.  It will be used semi-remotely 95% of the time so physical comfort is of minor concern. 

 

I am in a very dry area.  Summer monsoon moisture brings us to 35% rh on rare occasions.  We are typically at or less than 15% rh.  I will try to achieve some "sealing" but primarily as a critter barrier.  Vapor barrier will be discussed.  The dome provides free flow of air in and out but has a "brush" surround for dust and critters.  The fan will move 600cfm out of building.  There will be two filtered 16"x8" intake vents on the east and west walls about 2' off the ground.  So ideally I will turn on the fan and open the dome before sunset (will need to fine tune that).  Scope fans will be turned on when interior temp is less than outside temp (will need to fine tune that as well).  I also have a good fan to circulate air inside.

 

Radiant barrier is what I'm looking for.  John Manville AP foil faced sheathing sounds like it's a good option.  The reason is all about radiant heat prevention.  Perhaps more filtered vents would be prudent.   Yes..insulation is not what is needed. 

 

I have a dirt road that is about 1000feet from the observatory and is not too busy ~1 vehicle per hour during the day.  Enough dust is kicked up where filtering any air coming in will be a good idea.   I also have lot's of spiders,wasps and bees around.  So screens will be necessary at all intake points.

 

Good food for thought here...thanks

I didnt realize you had a dome and not a RoR. That does create some different scenarios with how it gets vented properly but I'm not familiar enough with a dome's build to give you advice on that. What other's have mentioned though sounds reasonable. Best of luck.



#10 kathyastro

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Posted 23 January 2020 - 05:46 PM

I have an 8' dome on a 10'x10' building.  I went with no insulation in the walls.  There is plenty of ventilation around the dome skirt.  On sunny summer days, the interior temperature might get 3-4 degrees Celsius above ambient.  I program my dome control software to open the dome at least an hour before imaging is to begin, and to rotate the opening so it is opposite the setting sun.  My indoor temperature is usually close to ambient when I start imaging.



#11 Peterson Engineering

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Posted 24 January 2020 - 08:55 AM

"My goal is to make the walls as thermally neutral as possible within reason."

 

OK, from an engineering viewpoint you're talking heat transfer.  There are 3 forms of heat transfer, radiation, convection and conduction.  The first two are germaine.

 

Solar radiation is best reflected by a white or mirrored surface.  I've got a white fiberglass TI home dome and white vinyl siding walls.  Found it to be highly effective in keeping the interior at ambient throughout the seasons.  Although it starts off shiny, I'd be leery about the use of aluminum.

 

Conduction is the flow of heat through material, such as the bottom of a pan on a stove top.  The more massive the structure the more heat it will retain when things cool down.  Keep the construction light weight.  Even concrete pads are bad.  My observatory is frame construction raised above the ground.

 

Convection is heat transfer by gas or liquid.  In this case allowing cooler air to flow through the observatory will help remove any heat that reaches the inside of the walls. The underside of my dome allows air movement to help keep the interior at ambient and to dissipate moisture.  The interior wall does have a 1/8" thick wallboard - a tradeoff between good appearance and just a little bit of thermal lag that's not really noticeable thanks to airflow.

 

Just about all of the advice given above is good.

 

Pete


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#12 GrandadCast

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Posted 26 January 2020 - 12:24 AM

"drywall on the interior", there is no interior really. Moisture and drywall, something is going to give. Try plywood instead. You can tape it and use plastic wood filter just like working it as if it's joint compound. 

Jess



#13 Chucke

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Posted 27 January 2020 - 09:17 PM

Maybe the moisture resistant green board that is used in bathrooms?



#14 nmoushon

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Posted 27 January 2020 - 11:51 PM

"drywall on the interior", there is no interior really. Moisture and drywall, something is going to give. Try plywood instead. You can tape it and use plastic wood filter just like working it as if it's joint compound. 

Jess

Moisture and plywood are just as bad. Mold grows on both. With proper ventilation and rain protection there shouldnt be a moisture issue. The only reason a moisture barrier is used with insulated walls is that the dew point is now on the inside of the wall, not the outside. So the barrier helps with that issue. If there is no insulation the a moisture barrier isnt really needed...though it would hurt if you added it. 

 

Maybe the moisture resistant green board that is used in bathrooms?

This is a good option, though just a bit more expensive. But again, if you have proper ventilation then moisture shouldnt be an issue (even in bathrooms). If the OP has powered vents on most of the day it will be really hard for moisture to build up inside unless there is an active leak bringing in water from the outside. 



#15 GrandadCast

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Posted 28 January 2020 - 09:04 AM

Venting when close is one thing, I am saying once the roof is opened and the dew falls and or frost. Things get damp and regular sheet rock is not something I went with. Green bath sheetrock is very expensive. I used 1/4” subfloor plywood, very paneling like and smooth, and after taping and plastic wood fill, primed and painted. Plywood is way stronger and will withstand hits on the wall. 

Jess



#16 tedbnh

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Posted 29 July 2020 - 01:16 PM

I've just completed a 10x10' building with an 8' Exploradome on the top, near Phoenix.  

 

The walls are 5' high, made of sheathing, coated with roll-on stucco-looking finish.

 

Between the 2x4' studs I put unfaced pink fiberglass insulation.

 

Over that I put pegboard on the entire interior.  It is awesome to be able to hang stuff anywhere on the walls.  Way better than pegboard.

 

Floor is a 3 1/2" concrete slab.

 

Everything is great, except for heat coming through the dome and "shoulders" (adapter from round to square).

 

Does anyone have a recommendation for some kind of flexible insulation I can glue to the underside of the dome and adapter shoulders?

 

I cannot paint the outside white, due to local NPOA restrictions.  (But I like the tan color anyway).

 

EDIT:  I also added a 12" exhaust fan that you can see in the pic on the right side.  It runs on a timer and keeps air flowing in under the dome ring and out all day.  

 

Thanks,
Ted

Attached Thumbnails

  • Obs 1.jpg
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  • Obs 2.jpg

Edited by tedbnh, 29 July 2020 - 01:21 PM.

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#17 t-ara-fan

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Posted 31 July 2020 - 06:35 PM

 with drywall on the interior. 

IMHO the drywall will just add a ton of weight - literally. And the whole thing will take longer to cool down.

 

 



#18 tim53

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Posted 02 August 2020 - 10:34 AM

I've just completed a 10x10' building with an 8' Exploradome on the top, near Phoenix.  

 

The walls are 5' high, made of sheathing, coated with roll-on stucco-looking finish.

 

Between the 2x4' studs I put unfaced pink fiberglass insulation.

 

Over that I put pegboard on the entire interior.  It is awesome to be able to hang stuff anywhere on the walls.  Way better than pegboard.

 

Floor is a 3 1/2" concrete slab.

 

Everything is great, except for heat coming through the dome and "shoulders" (adapter from round to square).

 

Does anyone have a recommendation for some kind of flexible insulation I can glue to the underside of the dome and adapter shoulders?

 

I cannot paint the outside white, due to local NPOA restrictions.  (But I like the tan color anyway).

 

EDIT:  I also added a 12" exhaust fan that you can see in the pic on the right side.  It runs on a timer and keeps air flowing in under the dome ring and out all day.  

 

Thanks,
Ted

I love your last pic!  Happy astronomer surrounded by some really cool toys!  

 

For Cosmic Acres, Craig Drake (GMARS builder) added a small window AC unit to the north wall.  I've tried it out when it was in the high 90s out there last month.  It quickly cooled the observatory (ROR, in my case) to about 70 degrees.  I plan to set the temperature to the predicted evening temperatures, so the scope doesn't have to spend hours coming to thermal equillibrium.  



#19 macdonjh

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Posted 02 August 2020 - 03:03 PM

IMHO the drywall will just add a ton of weight - literally. And the whole thing will take longer to cool down.

George P Dunham subsequently posted he'll have a dome, so the drywall will likely only be on his fixed walls.  Doesn't seem like extra weight will have any effect there.  I don't notice it taking too long for my roll-off to cool after I open the roof, but you have a point for a dome.



#20 magsterone

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Posted 12 August 2020 - 06:56 PM

I have a 8x8 flip off roof obs. I have a thermo controlled 12” wall mounted exhaust fan. The roof is painted with a heat reflecting paint. I have a humidifier in it that keeps it around 50%-55% . I put in faced insulation with a plastic vapor barrier and inexpensive paneling. The issue is now it is definitely warmer in there. The peaked roof allows airflow but did I do the wrong thing here. Would it be better to remove all of that insulation. It gets very hot and humid here on the gulf coast.

#21 George P Dunham

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Posted 17 August 2020 - 12:45 PM

Follow up. 

This spring I had great temperature control in the observatory and little if any thermal currents in the ota.

This summer, with high temps into lower and mid 90's, fan running for 3-4 hours before sunset, my observations are:

1.  Temp inside and out about the same at start of fan

2.  I open dome shutter a little after sunset to increase outside air into observatory.  Inside temp about 5 degrees above outside.

3.  At the time I start imaging (about 2 hours after sunset), temp in and out are nearly the same.

4.  I have had 3-4 occasions this summer to check collimnation and with that I can see any thermal columns or turbulence in the OTA.  On these occasions, some is present but not terrible.

5.  Last night however, with average seeing (per naked eye evaluation), I noted a lot of turbulence during my focus runs.  I had not noted any variance of environmental factors.  Will follow up.

 

I have some loose fiberglass filter on the inlet vents that restrict flow slightly but the inside of the dome is relatively dust free (in a dusty enviroment).  I also have a similar filter on the outside of my exhaust fan (to keep critters out).  The fan is 650cfm but I think the filtering cuts down that flow a bit.  

 

We are going to peak at 94f this week (pretty hot for 6800ft).  Terrible smoke and a new moon.  Not sure how to use this time.  Might spend a little time evaluating thermals inside the OTA. 

 

I had planned on buying a small free standing "air conditioner" for the observatory to try and keep the interior closer to the target imaging start temp but I am not sure it would be useful.

 

All in all, I am very happy with my design and methods to mitigate thermal ill effects in the observatory and in the OTA.

(10x10' building, 1" foam with reflective aluminum on one side on the sun facing walls under siding and 1/4" wood panel interior walls.  Two 4x12" exterior intake vents and one 10" 650cfm fan.  The observatory is otherwise sealed except for the 1" gap of the dome with a think brush weather barrier.



#22 ssagerian

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Posted 17 August 2020 - 01:19 PM

Hi George, sorry for being late to this thread, I didnt see any mention of the outside siding color or texture of the building? Just curious..



#23 George P Dunham

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Posted 17 August 2020 - 05:42 PM

James Hardey siding.  Off white desert color. 




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