Been lurking for awhile but I’ve got a question I’d like answered.
We are renovating an unheated side porch (19’x7′). There was a leak in the metal roof flashing which has now been fixed and we are starting to put the inside of the porch back together. I would like to add some insulation as the porch is south facing. The house was built in 1880s and the porch probably about 1900. The decking is 2×12 or larger with a metal roof at a 4/12 pitch to the side of the house. Since there is no venting, I’m thinking of using pink styrofoam against the underside of the decking before putting up the finished ceiling. I don’t want to use batt insulation due to the unvented roof and potential moisture buildup.
Am I on the right track? I live in Ottawa, Canada and temps go down to -30C (-22F) or so in winter. I’m thinking that by adding insulation while we have the inside opened up, we’ll get closer to three seasons use out of the porch with all the sun coming in.
Any feedback would be appreciated.
Cheers,
Wes
Replies
You don't need venting there as long as it is unheated. There is no energy to drive moist air up and there is little temperture differential between inside and out.
but is ounds like once you have insulation there, you are going to be tempted to heat it, right?
I still wouldn't worry about it for a three season day rooom
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Nope, no plans to heat it. Right now there can be as much as a 10C or more delta above the outside temperature. In late March and April, if it's 5C outside it's a comfortable 15C or better in the porch to read the paper and have a morning coffee with a sweater. My thought is insulating will add a couple/four weeks to either end of the spring/fall season. I think styrofoam on the ceiling and batts in the wall will extend the use by a bit. I'm just unsure if I'll be creating any other problems in the process. I guess I could just pretend it's an interior space and do the usual VB along with insulation and then I should be OK.
The pink will also shrug off getting wet, where FG is a huge headache. For super R rating cut 3" to fit between the rafters and then overlay the whole frame with 1". This has the advantage of sealing all those wood/insulation gaps plus it really stops infiltration.
The pink will need a sheetrock covering for fire.
I'd love to fill the gap between rafters but I'd have to add 6" first before adding the final 1" as the rafters are dimensional 2x6 rough sawn lumber. Mind you it would have a super R rating as you say.Now you mention I have to sheetrock over it for fire but does it have to be sheetrock? I thought any finished ceiling would do as long as the styrofoam isn't exposed? Maybe I need to do some more reading.
Actually, even heating isn't a problem. It's generating moisture that's the problem. People do it, cooking does it, furnaces with humidifiers do it.
What about the floor?
The floor is concrete slab. The old wood floor was long ago removed. I would assume no insulation under the slab. The floor is even sloped away from the house from the days when the porch wasn't enclosed.