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.
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.
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.
Need a location for questions like this. http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table
Post a picture of your soffit area outside.
Smart roof vents can be added to the roof, or round snap in vents can be added to the blocking between the rafters.
Not sure what the house is sided with have to do with venting issues.
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.
In this particular case drip edge vent is off the table because the OP has an exposed overhang.
He can install that smart vent as far up the roof line as he needs to get inside.
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.
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.
If the blocking between rafters are removed should brackets be installed? I don't see any brackets in place now and assumed the blocking was proving support and strength.
They should run from the gutter to the ridge. They are secured to the outside wall top plate by a "bird's mouth" cut and nailed. The same way just about any stick built roof system is.:thumbsup:
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?
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?
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?
I got two vents installed on the north side. Looks a little rough but should clean up when paint is touched up. Is more then four needed? Two on each side.
Turns out that the blocking wasn't really blocking but old ship lap siding.
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?
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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