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add soffit Vents to an Old House

I have an older house that has exposed eaves but no soffits.

I have just redone my roof and I installed a ridge vent
How do i go about adding vents to ventilate the attic
There appears to be solid blocking under the eave where
there would normally be space in a new house construction.
Can i install round soffits by drilling a hole into the blocking into the attic?

Re: add soffit Vents to an Old House

As a painting contractor, I often had to deal with the effects of undervented homes, i.e. peeling from ice dams and condensation running down rafters and dumping on boxed eaves.

The type of construction you describe on your house is common here in the Pacific Northwest. Lumber yards even stock pre-cut blocking with holes cut and screening already in place. I don't see why they can't be drilled after the fact, although unless you have a really good hole cutting bit, it is not fun. Stock circular venting plugs can be bought at your lumber yard or big box store. WWW.Ventmastersstore.com will give you a good idea of cost and net venting per hole. The louvers and/or screening of the hole, cuts the net venting area about in half, i.e. a 2-inch hole will only net you between 1.5 and 1.8 square inch of venting.

If you have the room, you might want to consider square louver vents, as the net venting area is greater. I think it would probably be easier to cut the square hole rather than all those circular holes. Also, the larger hole would be easier to help clear the air passage. Drilling the vent holes without clearing the insulation out of the way won't help the venting situation. You might still have to go into the attic to affix a baffle to assure that the passage stays free.

Generally, you want one square foot of venting area for every 300 feet of attic area. The ridge vents should be at least half of the net venting area. The goal is to have a natural convection current of cooler air rising to exit through the ridge vents, cooling the attic in general and keeping the roof sheathing cooler. Most shingle manufacturers will void their warrantees if your attic is not sufficiently vented.

Your eave vents should be equally distributed around the perimeter, so as to avoid hot spots or moist areas.

I am sure some of the other contributors here will add to these observations. There are several very competant carpentry contractors on this site. This humble painter yields to their expertise.

Re: add soffit Vents to an Old House

My roof survived with no venting for 86 years, appears to have the original roof deck and shingle life wasn't an issue when they had asbestos in them. I love seeing 60+ year old roofs still in service, but you're lucky to get 20 out of the new stuff.

But old houses were designed that way. Attic venting is a relatively newer (last 60 years) concept. Then again, so is insulation.

For round vents you can use a hole saw. You can cut through wood pretty fast with a hole saw. Easier than a reciprocating saw for square holes I think.

But as mentioned, you'll need a LOT of them.

Re: add soffit Vents to an Old House

if your well practiced with a circ saw and have a proper scaffold set up which is very stable, you could make square openings via plunge cutting which would be 3x faster than drilling or using a recip. plus by plunge cutting you can better control the depth of cut

Re: add soffit Vents to an Old House

One of the reasons older houses didn't need modern venting is that they leaked air like sieves. Roof and siding sheathing was of board stock with gaps all over. Wall structures were often of balloon construction with no fire/air barriers from the cellar to the attic. Insulation and vapor barriers were just about non-existant. Often the only vapor barrier was the paint on the outside of the siding -and it peeled!

Re: add soffit Vents to an Old House

I had the same issue - 1890's Victorian. I would have loved to put in one long soffit vent, however I have rafter tails every 2 feet which prevented me from doing that. So I drilled a 3" hole in every rafter "bay" (about 24 if I remember) and installed (caulked and tappled in) a plastic vent in each hole (sold in bulk at HD). In addition installed a ridge vent and gutter cables.

I had bad ice damns last year and was not about to have the same problem again. In a couple weeks will blow in insulation to cover the attic floor.

If that doesn't fix the problem, not sure what else to do.

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