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What type of insulation under an outdoor deck frame with 2x8s?
Eric Dalpe
Sept. 15, 2020Updated: Sept. 22, 2020
I have a 11x17 feet 3 season gazebo fully enclose on a deck. Sitting on deck board and finish the inside with LVT. I want to insulate the floor. Though of Rockwool for 2x8 but cant find any would going with 2x6 will make a big difference? I though of covering the wool with 1" rigid board to close it off and limit rodent. I m in Quebec Canada so winters are cold.
The walls are aluminium, i though I could insulate them with 1.5 " rigid board and cover with 1/2" pine. Should I put a vapor barrier in between?
Thanks
Eric
You have a couple of questions here, I will try to answer but I’ll have some of my own.
Given that your gazebo is exposed all around, you have all surfaces to insulate – floor, walls, roof. I don’t think going from 7.5” to 5.5” thick of Rockwool insulation is a problem, the bigger concern I’d have is only having 1.5” in the walls. Any way you can thicken that? And are you planning to heat it constantly or is this something you would heat up for occasional use?
Typical construction techniques should apply though, so yes to a vapor barrier on the interior of the insulation before you do pine. And keep in mind that aluminum will be a thermal bridge and cause heat loss, so putting insulation between metal will reduce the performance even more.
What about adding a thicker layer on the interior? I’m wondering if maybe you can attache strapping to the current metal ‘studs’ in some way to provide a nailing surface. That way you could possibly install a thicker layer, then vapour barrier and strapping and Pine. Does that make any sense? And can you spare any space on the interior?
Hi Mike, thanks for the reply. This is a 3 season gazebo with 5 tempered glass doors and angle roof. The roof is made of pine, war paper and sheet metal panels. I wont isolate the roof. This is for occasional use and I have a Carbon Infrared heater.
I agree the 6 inch bat would work and will add 1" rigid board on top of the 2x8 studs. I Just hope the 1.5 inch of space left on the 2x8 (7 1/2") wont cause any problem or fall down on the rigid board. No vapor I read under the floor correct?
The walls are panel of aluminium and wood 2x4. I will have to cut the rigid board to insert between the horizontal 2x4. The walls have 1.5 " space. If I go 2" it could work but with the 1/2 " pine Im losing 1" of wall not a big deal I guess. So 2 inch foam, vapor barier than pine? Wish I could add a picture.
Thanks for your help
So here are some more thoughts Eric – If you aren’t insulating the roof then I wouldn’t bother going too crazy anywhere else. May as well do the walls with a bit of insulation since you plan to add pine anyway, but you’d lose a lot of heat through the ceiling. Warm air rises and with no insulation in the roof, the floor insulation won’t make a big difference, so certainly don’t concern yourself over the thickness I would say.
But, that said – for occasional use and specifically with an infrared heater (which is a pretty efficient way to keep people warm in an enclosed space) I wouldn’t worry too much. Heating with electricity where there is clean energy like in Quebec makes a difference too, especially with an occasional use room like you are talking about. In your case, the carbon footprint of insulation as well as the cost of buying it starts to add up, so adding thick insulation in the floor won’t help you save money or energy I think.
I may even be so bold as to say an occasionally-used gazebo in Quebec with an infrared heater would have a lower carbon footprint than a campfire. It's starting to sound a bit like an emergency Covid Socialization room, am I right ? Don’t lose sleep however you choose to do it.
Hi Mike, I just your reply I had no notification you did so.
I see your point here and yes its more to work outside for a few hours, kids doing homework, dinners when sunny.
Heated floors would of been the best but you think insulation wont do much. I saw somewhere to sandwitch the rockwool between 1.5 in of rigid board ( under the decking and over the 2x8 stud)?
I was planning to get the material tomorrow so dont want to spend $ for nothing.
I guess the floor with 2x6 rockwool overed with OSB would do then? Any vapor before the OSB? I read the vinyl floor act as a Vapor barrier.
The walls I will go 2 inch, vapor and pine.
The celling is all pine finish.
Thanks for your help.
Eric