OT: Construction question - finishing an attic but making sure it's properly vented

[veggieburger]

I'll get straight to the point: our house has a massive unfinished attic with cathedral ceilings, and I would like to turn it into my man cave/spin room. I have confirmed that existing joists will support a floor.

I will hire someone to do the work, but I just need to understand- obviously we can't just slap down plywood and flooring, then spray foam the exposed inner roof. The soffits have to breath and pull the air out the top.

So what's the best way to jig this? Build knee walls (essentially a room with the attic) and let the air run as-is? Or is there a better way that allows me to maintain and capture more attic space?

Also, the insulation that's currently in the floor - will that have to be removed, or is it Ok just covering it over?

THANK YOU!

[572cv]

This post needs pictures (!), and perhaps some estimate of dimensions.

If the insulation in the floor is between the joists, it does not have to be removed. At the least, I would plan on a new floor system in the room that isolated the vibration from the new floor from the (bed?)rooms below.

A side note on the insulation: Is it old? is there any vermiculite there? Don't mess with that stuff, it is hazardous (asbestos containing) and should be removed if needed by professionals with experience. It will cost some real moolah if that is needed.

[echelon_john]

You can extend the insulated/conditioned “envelope” to include the whole space by sealing it and installing spray foam under the roof itself. You would remove the floor insulation in this case, and you’d want to consider extending heating/cooling to the room.

[veggieburger]

This post needs pictures (!), and perhaps some estimate of dimensions.

If the insulation in the floor is between the joists, it does not have to be removed. At the least, I would plan on a new floor system in the room that isolated the vibration from the new floor from the (bed?)rooms below.

A side note on the insulation: Is it old? is there any vermiculite there? Don't mess with that stuff, it is hazardous (asbestos containing) and should be removed if needed by professionals with experience. It will cost some real moolah if that is needed.

Insulation is Ok, had that checked - thanks!

Will post pictures at some point in the not too distant future!

[cmg]

To let the soffits breathe there will need to be air gap maintained to the ridge vent or upper vent. There are form board inserts that can provide that. If you have 6in rafter you could put r30 (around 4 in thick ) insulation between the rafters that would allow the air gap to be maintained. there are some youtubers building an A-frame house in the wilderness. they demonstrate how to spray foam while letting the roof deck breath using foam board inserts. It's about letting the condensation that forms a way to exit otherwise mold or rot will begin.

[yinzerniner]

You can extend the insulated/conditioned “envelope” to include the whole space by sealing it and installing spray foam under the roof itself. You would remove the floor insulation in this case, and you’d want to consider extending heating/cooling to the room.

Still need a LOT more info from the OP to judge the best course of action. Spray insulation is NOT the end-all be-all, and depending on the current roof configuration there might be better methods to get appropriate venting AND insulation.

-Need to do an inspection to judge how sound the roof sheathing and existing finished roofing is. Shingles and/or sheathing might need some replacements, which is easier done while other work is performed.
-Min code for sloped ceilings is 5' at lowest point, but in terms of actual usability you're better off going with 6' at lowest point. Much lower risk of bumping your head, less finished material cost, less conditioned space, etc.
-Need to have someone do calcs and locations for intake/exhaust, vapor barriers, insulation needed, etc. Since you're up north the min is R49 which gets really pricey with spray foam, and really thick with batts or rigid.

Basically, not enough to make an informed assessment.

[veggieburger]

To let the soffits breathe there will need to be air gap maintained to the ridge vent or upper vent. There are form board inserts that can provide that. If you have 6in rafter you could put r30 (around 4 in thick ) insulation between the rafters that would allow the air gap to be maintained. there are some youtubers building an A-frame house in the wilderness. they demonstrate how to spray foam while letting the roof deck breath using foam board inserts. It's about letting the condensation that forms a way to exit otherwise mold or rot will begin.

That's excellent - and the pic makes perfect sense. Thank you!!

[chris7ed]

I'm considering more insulation and will insulate a new addition. Spray foam was an option but after researching it I will likely use rockwool and cellulose.

[froze]

I'm assuming you got permits before you started, and you made sure the attic will meet all building codes for joist, ceiling, electrical, heating and air, as well egress is to code. If you build without permits and some time later the city or county finds out you did the work without permit you could be in huge trouble.

You got good advice on the insulation and soffit stuff. If you plan on using it during the summer I would put at least a couple of powered vents that will come on automatically when the temp inside the attic gets up to whatever preset temp you decide...unless you plan on air conditioning it, AND IF the floor of the attic is extremely well sealed so you don't pull air conditioned air out of the house which in turn will make your AC work harder which means more money being spent to cool the house, but instead the fans pull ambient air from outside. So ventilation fans can be good but mostly they're bad if not done right and a lot of people don't do them right. Fans is a controversial thing, some support it 100% and others don't support it 100%, but those that don't support it know that most people don't seal off the attic living space and thus all the issues.

We had a house that was very well insulated, so we installed a whole house fan and non powered whirly type of ventilators, so when the cool of the evening and night came on we turned on the whole house fan and opened windows on the far side of the house, the fan drew the cool air through the house and up into the attic where the whirly fans would start to spin and take the hot air out of the house. This could work in a living space but when the fan is on it makes it quite loud inside the attic, but we had a room in the attic that we used for short periods of time only because the room wasn't really necessary, but the fan did keep the room relatively cool, there was no AC in our room so in the summer it usually got to hot to go into that room unless the evening cool air came and we could blow the hot air out. We were living in a arid climate at the time. Just a thought which may not apply to your application.

[11.4]

For such a home improvement in a cold climate, this is much more complicated than it looks. Assuming you've dealt with load, stability, proper lateral bracing, septic capacity, and a dozen other issues, the big white elephant in the room is how to manage humidity. A house needs to be engineered around the particulars of the house. There's no way to make any kind of suggestion or comment without seeing detailed schematics and architectural drawings, knowing exactly how moisture is managed in the rest of the house, and knowing nearby tree cover, local wind flows, and the like. I don't mean it to sound pedantic, but the big evolution in home design and remodel in the past thirty or forty years has been about moisture management. There are countless new products coming out to manage humidity and heat, plus you're getting tougher and tougher permitting and zoning restrictions. Pay an engineer to evaluate your home -- around $1500 to $3000 in many municipalities and ideally give you a certified analysis (which may cost another couple thousand) that you and a contractor can rely on. I've done it both ways. I can assure you of which one was less expensive in the long run, gave better results, and shortened my lifespan the least.

[NHAero]

This is part of my field of work, but there's a lot of considerations. You can do vented or unvented, and both can work.

I'd suggest doing some searching on the Green Building Advisor web site, looking for articles by Martin Holladay and Peter Yost, on finishing an attic in a cold climate with proper thermal, air, and moisture management.

Perhaps the best compendium of information of all on these topics is at buildingscience.com. I'm sure there's great info on exactly what you're looking for.

[Mikej]

That's excellent - and the pic makes perfect sense. Thank you!!

Also, to add to the above, you could add 1" + to the 2x6 to achieve a higher R value. But definitely vent as the picture shows. I will also assist with ice prevention on your roof from heat transfer.

[batman1425]

Another thought - consider a radiant barrier along with the batting. Helps normalize the temperature swings during the day and keeps your attic from turning into an oven in the summer.

[bigman]

Listen to echelon john
- seal all the vents - spray foam the underside of the roof sheathing flush with the joists - or if room allows go over the joists - furr out a celing and you'll save tons on energy.

[yinzerniner]

Listen to echelon john
- seal all the vents - spray foam the underside of the roof sheathing flush with the joists - or if room allows go over the joists - furr out a celing and you'll save tons on energy.

Can't recommend against this strongly enough.

Without knowing the EXACT existing building conditions and the extant outside environment, haphazardly throwing out a single method will do way more damage than good.

Just throwing out ideas on how the OP should renovate their attic space with the minimal details provided would be like picking someones entire bike and riding kit while only knowing their height and weight, except 10x more expensive and 50x the annual running costs.

Unless you're used to doing this (ie contractor, architect, builder, experienced DIY'er with a long history in renovations and a background in construction) get help. It's not worth the hassle since it's not like you can put a house in the corner and forget about it.

[cmg]

the point of ventilation is to minimize the development of condensation by allowing air movement. The problem of spraying the foam on the bottom side of the roof deck is that it seals the deck and any humidity/condensation that forms does not have a way out. Do some research on insulating in a cold climate. There is way to spray the underside but it will have to treated first.

as previously suggested doing some research on the Green Building Advisor web site, looking for articles by Martin Holladay and Peter Yost, on finishing an attic in a cold climate with proper thermal, air, moisture management and buildingscience.com.

[adampaiva]

I'm not going to contest any one's expert opinions but at my A-frame cabin, after reading many differing internet opinions, I went with what I think was called a hot roof design. Stripped out the original fiberglass insulation and killed many mice in the process, sprayed a few inches of closed cell spray foam
https://farm8.staticflickr.com/7554/29489384915_8bcf1a51c8_z.jpg
w/ the help of the girlfriend
https://farm9.staticflickr.com/8036/29489380355_fcbdcf198f_z.jpg
installed plasterboard onto the underside of the roof rafters
https://farm5.staticflickr.com/4694/26340405428_d4e26116d1_z.jpg
and then threw on a standing seam metal roof on top of the old asphalt shingles, furred out with 2x4s, + a layer plywood and roof underlayment
https://farm5.staticflickr.com/4840/44338178260_d76e4a3676_z.jpg

[adampaiva]

next up is siding...

[veggieburger]

I'm not going to contest any one's expert opinions but at my A-frame cabin, after reading many differing internet opinions, I went with what I think was called a hot roof design. Stripped out the original fiberglass insulation and killed many mice in the process, sprayed a few inches of closed cell spray foam

THAT'S AMAZING. Adopt me?

[cmg]

"then threw on a standing seam metal roof on top of the old asphalt shingles, furred out with 2x4s, + a layer plywood and roof underlayment" If you used a ridge vent and had vents at the bottom of your "A" you have created a space to let the roof breathe/ vent.