Insulating attic, summer only


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Old 08-19-20, 04:25 PM
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Insulating attic, summer only

Hello experts,

I have this cottage with an unfinished roof. Of course very hot in the summer with the sun pounding onto the roof all day long.
My goal is to somehow insulate area against summer heat only as we are not there during the winter.
May eventually put a window AC up there.
What’s the most economical way to accomplish this ?
Should I go with full insulation, vapour barrier etc or go with the bubble stuff ?

ANY input is appreciated.
thanks all
Harold






 
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Old 08-19-20, 04:58 PM
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Well, sad to say with that method of construction (no ventilation, no attic) insulation alone isnt going to keep the heat out. It's going to be hot up there no matter what, so an AC is a must have, IMO. What will happen is that the insulation will slow the heat from coming in, but it won't stop it. Once it finally does get hot up there, insulation keeps heat in just as well as it keeps heat out, so unless the AC is on, you will notice that it will probably stay warm up there longer in the evening than before because the insulation slows heat loss. But the purpose of insulation would be to make it easier to condition (heat or cool, depending on the season). If that is your goal, then anything will be better than nothing.

I think if you want the most R value, you would want to rip sheets of rigid insulation on a table saw to fit snugly between the rafters, then seal the edges. You could use 1", 1 1/2", 2", or 3" foam, depending on how much R Value you want. And you could put 1 or 2 layers of that against the roof deck, depending. IMO 2" would be the bare minimum you would want up there... 3 or 4" if possible. Then under that you could staple up some fiberglass insulation just to fill the remaining space.

Insulation is ALWAYS more effective if it has an air barrier (drywall) over it, so give that some thought too. Having no air barrier can create problems, such as during winter months. You don't want warm moist air (which naturally rises) coming into contact with a cold, snow covered roof, for example. Once you insulate the rafters, the roof deck will stay colder than it did before, creating a larger difference in temperature. Condensation and mold could be problems without an air barrier over the insulation.
 
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Old 08-20-20, 04:59 AM
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Thank you so much for your input.
Harold
 
 

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