help with ideas for passive cooling...

[psychob0b1977]

Hi guys,

I have a good sized shed that i use for my workshop. it is 8x20. it is un-insulated.

Summer is rapidly approaching and (ill get to winter some other time) it gets well over 100 degrees inside this thing during the hottest days of the season.

Last year we had a few days that were about 100* outside and it must have been 120+ inside the shed. even on days of high 70s+ it becomes un-bearable.

there are no windows at all, except in the door. and there is 1 double door on the west end of the building. so i dont seem to have any way to remove the excess heat.

The problem i have is money is tight. (isn't it always?) so i need to go the most bang for the buck route and i have a budget of about $100 TOTAL. (so a mini split is out)

I was thinking of insulating the roof, i can get r19 insulation for the 2x6 rafters at a total cost of $107 which would eat my entire budget for this project. or i can get R13 insulation for about $60 leaving a little room for some thing else.

So should i get the R19, or the R13?

If i get the r13 i can also possibly get an exhaust fan or some sort of vent. If i do go the vent route, whats the best way to remove all that extra heat? ridge vent is out, the cost is too much. roof vents are out too because i dont want to have any holes in my roof deck. so i guess that leaves gable vents or powered vents?

I was thinking about installing a gable vent on either end of the shed to create (hopefully) a cross breeze. but due to the construction of the gable ends, the vents will be small and off center. so i dont know if they will be effective?

Sorry for such a long post, i'm kind of thinking out loud here!

I'll take a few pics tonight to show exactly what I'm working with.

 

[rsanter]

Easy. Keep the sun off of it
Build a secondary roof or cover. Plant trees...etc

Years ago I built a shed like a small house to hold things I didn't have room for in the house but cared more about than to put them in a garden shed.

I built a 12x12 on a raised platform
No insulation
Drilled holes in the top and bottom plates of the walls
Did drywall inside and along the rafters
Installed large gable vents

What would happen is that when the sun hit it it would transfer heat into the air in the air gap. That hotter air would rise and pull cooler air in from ground level.
That shed always stayed cooler than the outside.

Downside.
Does not really retain heat in the winter but what I was storing was more heat sensitive and the cold didn't bother it

Bob

 

[pseudorealityx]

"I can't afford to actually cool the space, and I don't want to cut holes where the hot air is."


Yeah... work at night.

 

[psychob0b1977]

Easy. Keep the sun off of it
Build a secondary roof or cover. Plant trees...etc

Years ago I built a shed like a small house to hold things I didn't have room for in the house but cared more about than to put them in a garden shed.

I built a 12x12 on a raised platform
No insulation
Drilled holes in the top and bottom plates of the walls
Did drywall inside and along the rafters
Installed large gable vents

What would happen is that when the sun hit it it would transfer heat into the air in the air gap. That hotter air would rise and pull cooler air in from ground level.
That shed always stayed cooler than the outside.

Downside.
Does not really retain heat in the winter but what I was storing was more heat sensitive and the cold didn't bother it

Bob

So you had no insulation at all? Even in the rafters?

Working at night isn't an option either as it will maintain 100° all night long.

I was thinking that putting insulation (of any r value) will keep some heat out, and 2 gable vents would remove some/all of the heat that gets past the insulation.

I'm not asking for a lot, I'm not expecting 65° at noon when it's 95° out side. I'd be tickled pink if I could get this place down to the outside temp.

Right now it has temps of 20°+ the outside temperature.

 

[Highbeam]

I would rather have R-13 all around than R-19 in the roof only.

 

[Falcon67]

Ridge venting is only $10 per 4' at HD, so you could do that a section at a time if you wanted. I would be looking at doing 8' of ridge or so at a time and filling those rafter bays with R13 to leave an air space for air to move from the eves to the ridge - assuming the building has eves at all.

If not, then R13 everywhere and out a exhaust/attic fan high in the north end, run it at night to pull in night air to cool the mass in the space. The attic fan will bust your budget, so I would start with R13 everywhere and make do after that. You're going to have to have another hole in the building for a window and/or fan - ask around the lumber yards for a scratch and dent window of some size. My old shop had two 24x60 bronze double pane insulated glass single hung windows - scratched up but functional, $25 each. New around $175 each. They asked $50, I said I'll take both at $25. Shop around, you never know. Never hurts to ask. Also - look for used building material places or a local Habitat store.

Passive cooling is going to primarily be using cool night air to chill a large mass that then radiates the cold. My 64,000lb slab does a good job of that - I open two windows, cheap box fan in a north window and let it run all night. Until it gets in the 80s, low 90s all night, then I give up and run the AC. Cheap mass for you might be 55 gallon barrels full of water.

 

[psychob0b1977]

Ridge venting is only $10 per 4' at HD, so you could do that a section at a time if you wanted. I would be looking at doing 8' of ridge or so at a time and filling those rafter bays with R13 to leave an air space for air to move from the eves to the ridge - assuming the building has eves at all.

If not, then R13 everywhere and out a exhaust/attic fan high in the north end, run it at night to pull in night air to cool the mass in the space. The attic fan will bust your budget, so I would start with R13 everywhere and make do after that. You're going to have to have another hole in the building for a window and/or fan - ask around the lumber yards for a scratch and dent window of some size. My old shop had two 24x60 bronze double pane insulated glass single hung windows - scratched up but functional, $25 each. New around $175 each. They asked $50, I said I'll take both at $25. Shop around, you never know. Never hurts to ask. Also - look for used building material places or a local Habitat store.

Passive cooling is going to primarily be using cool night air to chill a large mass that then radiates the cold. My 64,000lb slab does a good job of that - I open two windows, cheap box fan in a north window and let it run all night. Until it gets in the 80s, low 90s all night, then I give up and run the AC. Cheap mass for you might be 55 gallon barrels full of water.

Thanks for the ideas, I'll have to check the re store near me, I always forget about that place...

I think the reason it stays so hot inside this shed is because all the stuff gets super heated and just keeps radiating heat. That and there is no ventilation... it's a shed, not a garage, so I don't have the luxury of opening 2 big bay doors. I only open up 1 29"door. At best I can open the other half of the double door, and believe me, it doesn't help. Even on a windy day I can stand just a foot or 2 inside the shed with the doors open and feel no breeze.

I think I'm going to go ahead and insulate the roof with the r13 to help keep some heat out where it belongs. Then I need to install some sort of vent or a small window that will let the heat that does get in, out.

Thanks

 

[TEKCRAFT]

Do you have a shovel and a strong back (or a friend with a trencher)? One solution is tempered air cooling. This was used here in the 1800's and today in third-world countries.
Basically, its a tube burried 2-3 ft deep that air is drawn through to cool the building. A low cost tube is flexible plastic drainage tile (without the slots) that can be buried and run to a couple locations in the building. A small fan can be used to draw the air, and use a roof vent as previously mentioned to get the hot air out.
I laid a serpentine pattern of rigid PVC under a friend's workshop (laid before the slab was poured), and this worked great.

 

[Fun pain]

Radiant barrier under the roof and anywhere sun light hits the building would help alot as well.

If it was me, I would radiant barrier the inside of the roof. Double bubble between the rafters. Slap up a ceiling 2Ft on center. 10 2x4's @ $3. Drywall. 5 sheets @ $7. Cellulose at R19 for 8x10 would be 4 bags. $5 buck a bag.

$30+$35+$20= $85

If you bought just 3 more bags of cellulose (right at $100). The r-value would be more like R30


I like TEKCRAFT's old idea! I am going to go even older. Egyptians used wet tappestries over window openings so when the wind blew it would passively cool there homes. Most Cali, residence around LA area do it this way today, Swamp Cooler, but it kinda stops working at like 40% humidity. Box fan and a wet towel may work.

 

[theoldwizard1]

Easy. Keep the sun off of it
Build a secondary roof or cover. Plant trees...etc

Tarp, with at least 1' of air space between it and the roof. Cheap, effective and ugly.

 

[TOOL_MONGER]

Do you have power close? I envision your situation and I see myself finding a squirrel cage blower and having it circulate some air...

 

[dogdog]

If you can move the garage door facing south east and have an opening at back or top of roof for air flow. That would be passive.....

 

[Mustang51js]

Put a attic fan on the gable and install it on a switch so it doesn't run when your not in there. And do the insulation and vents like posted

 

[volleyball]

What about winter? I hear a lot of cooling ideas, many which won't work in humid Ma.,which would ruin the building in winter.
The radiant foils is the only appropriate option so far mentioned.
If it is getting that hot, it has to be in direct sun with a dark roof color. Bad idea. And it's is not 120 after 10 but it might be too late to work then.
Why has no one mentioned windows? Get a couple of grossmans oddball windows, or get some used windows, they don't have to be double pane, or even basement windows to put in on opposite walls where the air does flow. A simple box fan to aid flow.
Get some white or silver metal panels and put them on the roof with spacing between existing roof and new panels. Air will flow and the metal will reflect most of the heat.
Any mister idea will not work. That is for arid locations only, like the Egyptian desert.

 

[NUTTSGT]

Since you are a tight budget, I'd put some R13 in the ceiling and add some gable vents to get cross ventilation. Any left over funds, add some R13 in the walls.

While your current budget might be $100, you need to continue that adding to that budget as time goes on. A mini-roll of R13 generally costs about 10 bucks. Pick one here and there and you can easily get the walls insulated during the summer.