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Attic venting issues

3K views 22 replies 6 participants last post by  Gary in WA 
#1 ·
I'm looking for ideas on adding venting to attic.

Info on house is a 1920's cape cod. Finished "second floor".

I added gable vents one on each side on the top peak section above the finished space. Then there are foam baffles on the ceiling slanted section going down to the knee wall section.

The issue is there is no form of intake of air. There are no soffit vents due to exposed rafters. Now the real trick is asbestos cement board siding.

So I am just looking for some ideas on getting some better venting in the attic.

Thanks
 
#7 ·
I suppose if he isn't wedded to the exposed overhang he could close it off, by knocking out the blockers in between the rafters and installing a vented soffit. That could be wood with a continuous soffit vent. That could be done without touching the roof.
 
#19 ·
Really difficult to give an answer with your set-up... pictures would help. Sounds like you need some venting on the North side for sure. Figure 1/150 to be safe. Add up the intake net-free area and the top- exhaust NFVA, they should be equal to be most effective.

Gary
 
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#2 ·
#4 ·
The link below provides one solution to your issue. Joecaption mentioned them. I never used them personally but I once knew a professional roofer in Pennsylvania who swore by them. If you live in snow country they would make me nervous but this guy installed them in snow country.
If you did something like that you might complete the package by installing a ridge vent AND closing off your gable vents so they don't become an intake for the ridge.


http://www.dciproducts.com/html/smartvent.htm
 
#8 ·
The reason the siding type matters is because it would make it tough to drill out and not destroy the siding.

Location is south central PA.



Excuse the sloppy painting. It's another on going project.

I had one idea to removed the top row of siding. Drill holes through blocking between rafters instead of knocking them out since they look to be providing support to the rafters? Add blocking between rafters on the end to become a fascia board. Then add vented soffit.

I prefer to not have to mess with the roof any.
 
#10 ·
If you knock out the blockers completely that is your best bet. Adding a couple strips of wood to incorporate a continuous soffit vent will add any stabilizing needed to the underside of the rafters. By removing the blockers you can be sure of the air flow. Of course it means a fascia too and changes the whole look.
 
#15 ·


So probably the best bet is to remove top row of siding. Knock out the boards between rafters in attic. Add blocking in between rafters at end, since I would have to remove gutters to add a solid fascia board. Then install a vented soffit with a j channel to attach it I believe.

Since the rafters should be nailed there's no need to bracing? I just remember seeing new construction having brackets nailed to the side of the rafter and bends down and nails on the top plate?

Thanks
 
#16 ·
You don't need the blocking to prevent rafter rotation if under 2x10; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_par032.htm?bu2=undefined

IF you replace them with steel hold-downs per location code requirements- check locally; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_par041.htm?bu2=undefined
Don't forget to figure in the over-hang for resistance loads.

To drill them for 1/150 requires 3" holes; end-to-end, much better to use rectangular screened vents. Are you certain you need ventilation? Do you have mold (mildew)? Are the knee-wall gables vented on side-walls?

Gary
 
#17 ·
They are 2x6.

This last winter(first winter in house) I noticed moisture issues on the knee wall section on the north side. I have started trying to airseal any gaps and added a fan for a unvented bathroom.

Currently the only vents are the two gables I added in at the peaks. From the knee walls the only form of intake is a slight gap between blocking between rafters and the roof sheathing.

The north side attic has a vaulted stairway on one side so I could only add gable side walls to the front of the house which wouldn't look very good.

I think I might go for screens and knock out some blocking. I don't believe I need much venting. The knee wall floor space is probably no more than 360sqft then add in a slight gap on the slanted section and the tiny space in the peak.

Maybe knock out 2 blocks on each side. Give about 16x4 on each?
 
#21 ·
I would/have added gable vents at top of each end, behind the knee-walls, painted house color not to stand proud. 1/300 would probably do...

Gary
 
#22 ·
So add same style vents that's on the gable but on top section of knee wall attic space? I was thinking about painting the top gable when I do the second coat of paint on the house.

The gables show online 34 square inch of venting per vent. So that's 68 square inches of exhaust at the top.

The soffit vents I'm adding have 28 sq inch per vent. I was thinking 2 per side but open to the idea of more.

I believe I'm at about 390 sqft of attic space. Maybe less?
 
#23 ·
Problem is the attics are connected by the air chutes you mentioned earlier. Just add a ridge vent (as mentioned), soffit vent every (or every-other at min.) rafter bay, cover the fiberglass floor cavity AND back of knee-wall FG insulation with a housewrap (Tyvek= 58 perms) to prevent R-value loss/reduction of- by convective loops/wind-washing. Then remove/block gable vents as mentioned. Much better system as per work involved in soffit ventilation as planned. Air seal/canned foam any wall below- top plates/drywall-plaster joints, first. With your chutes already in place (as I had to reread) the hardest part of work is already done. Use new chutes to direct air over the FG floor if not using housewrap...

Gary
 
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