Author Topic: old house attic soffit venting issue  (Read 3937 times)

mathx

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old house attic soffit venting issue
« on: September 29, 2015, 12:23:14 AM »
I've got a sloped roof where the slope is expressed in the upstairs rooms as a curve from wall to ceiling. Nice character but bad because the roof is maybe 4" away from that curved wall face, very hot or cold with the seasons.

Worse, way down that overhanging section at the soffits, which seems to be about 3' beyond the edge of the attic floor, is loose bits of blown cellulose (I had the rest sucked out recently so I could fix wiring and put in a vapour barrier, and reinsulate (looking at wool batts!)). There was only about 4" of cellulose, old and dirty. Probably R8 at most!

Problem is twofold. Jerks who took out the cellulose shoulda got down into the soffit area to get it ALL out. 2ndly, some of the 'wells' are empty, I can see down, but see no daylight, and feel no ventilation coming in. Luckily there's two medium sized windows in the gables at the ends which I could replace with gable vents easily to vent the attic.

Would such vents be enough? They're not as 'low' down in the roof (about 1 foot above attic floor) as the soffits (which are almost 2 feet below attic floor). The lowest point is where you'd want air coming in which the gable vents wouldnt provide.

I have 4 8x8" square holes with metal cap vents for air egress from the roof. Is that enough? (Roof faces e-w, is about 7' tall above attic floor which is  22 feet wide by 30' long. Gets pretty hot on a sunny summer day.)

I can shopvac out the rest of the cellulose down in the soffits, but having air come in there would be ideal, but I forsee getting a tall ladder and detaching all my soffit panels and drilling holes in whatever board is blocking flow - a ton of work. Alternately, add the gable vents, and to achieve enough airflow, perhaps a powered fan blowing out the vent holes (there goes efficiency by wasting electricity...). I am going to put up some radiant barrier at least on the west facing slope side too to keep things cool in summer.

As for insulating the curved edge of the wall, not sure how to deal with that. If I give up with the soffit venting (though the underside of the roof down the soffit wells still needs air regardless, so I cant plug them up too much!) I can insulate a bit more on the wall side under the roof, but at 4" of clearance, I am not going to get much R in there, and I assume I need at least 1" of clearance for air, if I  reestablish soffit flow.

What's the best solution here?

[ Side note: why didnt I remove the dirty cellulose myself? a quick calculation of volume vs garbage bags + rodent droppings from prev infestation came to >75 garbage bags of material and a ton of work. it was better for me to take some side work in my regular day job to pay for it directly than to do it myself! :) ]

« Last Edit: September 29, 2015, 12:26:32 AM by mathx »

velocistar237

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Re: old house attic soffit venting issue
« Reply #1 on: September 29, 2015, 08:11:18 AM »
What's your winter like? Soffit vents combined with ridge or gable vents help keep the whole roof cold and prevent ice dams. Without soffit vents and with low insulation, you'll get warm spots and ice dams.

There are baffles you can install that keep insulation from blocking the soffit vents. If there's not enough room for insulation, you could use something with higher R per inch, like foam. Or jack up the roof.



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robartsd

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Re: old house attic soffit venting issue
« Reply #2 on: September 29, 2015, 01:43:02 PM »
If your concern is primarily venting heat in the summer, you won't get much gain from soffit vents vs. gable vents; but the roof does need enough airflow in the soffits to dry out. As velocistar237 pointed out, if you get snow on your roof it is critical that there are not warm spots that melt the snow only to refreeze lower down on your roof.

mathx

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Re: old house attic soffit venting issue
« Reply #3 on: September 29, 2015, 11:59:06 PM »
Canada, so cold winters. My issue is ensuring that there's airflow up under the roof for all reasons (cooling in summer, and ensuring no accumulation of moisture in the underside of the  roof). Obviously to do this correctly, I have to get into the bottomside of the soffits from outside and see what's going on there.

once im in there, Ill drill some holes anyway, then use soffit 'vents' (aka moore vents) to guide airflow along the roof bottom, and maintain a clear path for air thru the insulation. Just wondering
how many holes i need considering the vent sizes (4 8x8"), and if i need more vent holes for egress in my roof. (We do get hot summers with >95F/35C several days a summer, and the roof faces west so for cooling purposes as well).

Jacking up the roof seems like a lot of work (and I shoulda done it before it was just reshingled, I didnt have time with work duties to get it done and there were many holes leaking, so it had to be done quickly).  Ill probably jam some foam board to insulate that curved corner of the roof, if I can get at it... Hard to get in there cuz so many damn roofing nails came thru with the application of a layer of ply (because the old 'barnboards' of the roof had so many gaps, shingles couldnt be put down solidly.)

Thanks for the advice.



Noahjoe

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Re: old house attic soffit venting issue
« Reply #4 on: September 30, 2015, 08:41:28 AM »
mathx,

I just did this to my roof:

1. removed all cellulose from the floor, because I have usable attic space for storage/etc.
2. blocked all gable vents/insulated all walls. I put 1" foil faced foam (facing out), then r30 insulation, unfaced, then 1" foil faced foam (facing in). This gave me R42, and I also air sealed all gaps with great stuff (it's closed cell, and allowed me to do a little at a time).
3. DRILLED 3 3"holes in all soffit vents (the previous owner put in vented soffit over flippin' plywood, so it was more there for looks). I had this done when the house was reroofed though, so I spared myself from having to remove all the soffit to do it. The roofers just went in from the top. And at no additional cost!
    a. If you vent Gable/roof like it is now, you're not giving your attic appropriate breathing in your climate. I'm in Wisconsin, which is quite a bit tamer and this was the case for me.
4. I made my own soffit vents out of 1" foil faced foam (facing up towards the roof deck) spaced 1" from the roof boards (I glued 1" scraps from the foam sheets to do this). This allowed me to maximize my r-value. You could do it with 2" foam if you're made of money. I ran these vents ALL the way up to the roof vents, then created a ceiling out of the foam/insulation method mentioned earlier.
5. I air sealed all gaps with great stuff. I spent about 250 bucks on it for the whole attic (which was over 100 cans) but it was so, so, so, so worth it.
6. I had to fur down my trusses with a 2x6 to create a larger cavity. I then filled said cavity with R30 unfaced insulation. I held it in place with drywall shims (the long, thing cardboard strips).
7. I then put one more layer of foil-faced foam, with the foil facing into my attic (to reflect hot/cold from heat/air conditioning). This covered up all the fiberglass insulation.
8. I used aluminum tape to seal all the seams on the foil-faced foam. Essentially, the insulation is air sealed from both sides, and reflective material will radiate heat out and heat/cold in, which essentially gives me a better than R42 gain.

My attic went from R-19 (and an unvented attic ladder opening) to R42/fully air sealed and properly vented. My electric/gas bill was immediately cut in half, and this month my investment has officially paid for itself (not to mention the tax break I should get in the US). It's messy, shitty work and it took me about 50-75 man hours, but in the end my attic is properly vented, air sealed, and done well all for about $1,500 out of pocket. This was for a 600-700 square foot attic space with a 6/12 pitch.

mathx

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Re: old house attic soffit venting issue
« Reply #5 on: September 30, 2015, 11:09:44 PM »
@Noahjoe: is the foil-facing a vapour barrier as well? Might that not be an issue because if any moisture gets into the insulation (leak from top etc), it has no way to evaporate. Maybe not a big deal if it doesnt enclose any wood elements, but if it does, that could promote rot. Usually vapour barrier is one sided only, yes?

Wisconsin might have similar winters to us (im in S. Ontario, so -25F winters worst every 5 years and 102F summers max similarly, usually more like -10F/95F tho a heated roof is a lot warmer than that!).

Your job sounds pretty great, making a nice storage attic , I think we have a similar size. Issue is the only access is a roof hatch in a closet, not very accessible (ladder, etc, and we already
have too much crap stored in the basement, we have lots of storage space heh). Sounds like you had the same issue I have, totally sealed soffits :( So annoying. Takes lots of time to fix it properly ;(

I think now Im going to be fighting to beat the oncoming cold winters (into single digits C at nights now, ie < 50F) so the heat is coming on and I have no insulation! :) I can get the poly vapour barrier up quick and at least 1 layer of roxul batt (giving up on sheep's wool, its _7x_ more $$!) and still walk around on the joists to get to things while I fix it. Not sure if Ill just layer a 2nd layer of batt crosswise over that, or blow in (I dont dig the blown in stuff, and read that it mats down after a few years, and can be blown around ('wind washing') uncovering large areas of underlayer.

Question is, do I put the vapour barrier OVER the joist tops, or just staple up to below their top edge on each side, leaving the top to 'breathe'?

Noahjoe

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Re: old house attic soffit venting issue
« Reply #6 on: October 02, 2015, 09:09:28 AM »
mathx,

I'd imagine that if the roof leaked the water would follow the insulation panels down to the soffit and evaporate/drain on the way. I'm not TOO worry about it penetrating, as I was very persnickety in how I installed it. It's 100% sealed with a 6/12 pitch, so I'm hoping this isn't a realistic worry. And yes, the foil is my vapor barrier. I believe it's even rated as such.

Venting at the soffits will be worth it, even if it's a big pain in the ass. My gable vents weren't moving enough air and I had to deal with a little surface mold (granted, this insulation was probably about 22 years old, so it took a long time to happen). A fan could help that (but those alone are about 300 bucks) but I'd much prefer the roof is breathing really well. Especially so anywhere snow is a problem - ice dams are the worst.

Storage space was really only a secondary win. the big problem, to me, is that you will ALWAYS have a huge air leak where the ladder goes into your attic. Even with those foam covers, you're still losing a ton of R-value for a Canadian winter. The big win is that it's 100% air sealed and a consistent R-42 all around. You're never going to get that with cellulose or batts.

I'm not a professional, so take this for what it's worth: if I were blowing in onto my joists, I'd probably let the vapor barrier sag between the joists so I could fit more cellulose in. YMMV.