Custom Soffit vents, what tools do I need? - Woodworking Talk - Woodworkers Forum
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post #1 of 12 Old 11-10-2008, 12:23 AM Thread Starter
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Custom Soffit vents, what tools do I need?

I am planning on making custom soffit vents for my home that will go inbetween the rafter lookouts at the top of the wall cap. The home currently has no ventillation in the eaves. I am also planning on putting a ridge cap on the roof in the spring. Followed by blow in cellulose.

Between the rafters the space I have to work with is about 14" wide by 5.5" high. I picked up some 1-3/8" x 5/8" colonial stop molding from my local home depot. I plan to make a 12x5.5" frame which I will then staple copper screening to the back of and then nail/screw to the vent opening on the house.

I need to miter the corners of the trim, but all i have available at the moment is a hand saw and cheapo plastic jig, not accurate enough to make good miters. Corners come out with lots of gaps. I also sold my table saw a few years ago, so im rather limited on power tools now. But here are a few tools I have if they can be of use, circular saw, jig saw, & coping saw.

What would be the best or cheapest way to make good miters. Does it make sense to spend the $$$ on a compound miter saw? Or would buying a decent $$ manual miter saw work just as well but not break the bank?

By the way I will have to make upwards of 30 of these frames.

Any input is appreciated.
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post #2 of 12 Old 11-10-2008, 06:24 AM
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In the "old days" I have used (may even still have somewhere) the classic wooden miter box. Those are perfectly fine. That was all mankind had until just recently. There are still many, many houses in this country that were built with beautiful joinery before power tools were available.

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post #3 of 12 Old 11-10-2008, 06:33 AM
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George is right, a miter box properly used will give good results. It's a bit more labor intensive than a compound miter saw, but your time and budget controls that. You could conceivably make a left/right jig to be used with your circular saw. It would be cumbersome to use, and the wood to be cut would/should be placed upside down for the cleanest cut.

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post #4 of 12 Old 11-10-2008, 09:22 AM
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Nowwhatnapster Welcome to the forum. I agree with GeorgeC and Cabinetman. You can buy a small wooden or plastic miter box with hand saw anywhere from $10.00 to $25.00 and it will do what you need. Almost any lumber yard or hardware store would have one, and even some discount stores carry them. I picked a real little one up one time at a WalGreen Pharmicy for a couple of dollors. The miterbox was aluminum and it is the best little saw to cut shoe molding. Good luck.

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post #5 of 12 Old 11-10-2008, 11:33 AM
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They work good for cutting small diameter, short cutoffs of dowels also. You know the cuts that if you do it on a powered mitersaw the piece you want goes flying off out of sight. This is an antique mitersaw that I refurbished, I used a piece of Trex for the cut board.

Last edited by user4178; 11-10-2008 at 11:41 AM.
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post #6 of 12 Old 11-12-2008, 09:17 AM
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Sounds labor intensive but it will work. Are there bird blocks in the spaces between the rafter tails now or is it just open? If you are planning to blow in insulation you need to install baffles or the insulation will block the air flow. If there are bird blocks already in place you will have to do it from inside.
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post #7 of 12 Old 11-13-2008, 01:37 AM Thread Starter
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Thanks for all the responses. Looks like I will go pick up a decent miter box and start sawing then. Seems the most economical.

Woodchuck: I envy your antique miter box by the way. Nice find. It's hard to find well made tools like that.

mics_54: Currently between the rafters at the top of the wall there is just a solid plank of wood. No spaces for air movement. All the attic has for ventilation is two gable vents. one of which isnt even open. So im planning on cutting a rectangular hole into those blocks and making the custom soffit vents to fit over them.

As for the insulation, its gonna be blown in cellulose, and I will make sure I use baffles :-)
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post #8 of 12 Old 11-13-2008, 02:01 AM
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You did not note your location, but I would check
the pawn shops. I know several here have a miter
saws similar to the antique one but not that old
for $5 to $10, They were Craftsmans I think.
A little clean up and you could have a nice tool
that would last a life time.
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post #9 of 12 Old 11-14-2008, 10:32 AM
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roof ventilation

nowwhatnapster, I don't know what location you are or the local codes or your knowledge of construction of dwellings so I going to assume you don't know what the bird blocks are for. I wouldnt suggest that you remove the bird blocks or augment them in a great way as they are there for the primary purpose of keeping your rafters/trusses vertical. They usually do not close off the space entirely and I am at a loss as to why they were installed to close it off..if they do. I have to assume they do go all the way to the underside of your roof if you haven't mentioned any gap at the tops of the block. Generally speaking a roof requires a minimum amount of attic ventilation based on the total square footage of the roof and the local code requirements. Also generally speaking a 1" space at the top of the birdblocking, or a series of holes drilled through the blocks is adequate to satisfy the ventilation requirements. Removing too much of the blocks or making the ventilation holes too large is not suggested because you WANT insulation to cover the top plates of the walls and note that directly over the walls is the place in the entire structure that you will have the least amount of insulation because it is so close to the roof. You want to get as much insulation in this area as possible especially in colder climates. I drawn a sketch of a typical wall/roof section to illustrate placement of vent holes in the bird blocks. Once these holes are drilled or the spaces at the tops of the blocks are made you can cover the spaces or holes inside or out at your discretion. The spaces/holes should not be blocked by insulation and have free flow to the baffles. If you already know this information...maybe the others do not. Cheers

Custom Soffit vents, what tools do I need?-wall-section.jpg

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post #10 of 12 Old 12-28-2008, 12:19 AM Thread Starter
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First sorry for the delay in the response, got caught up with work and life, haven't had time to work on projects.

mics_54, I have done a bit of research, however, I will admit you are the first person to tell me that the bird blocks are their to keep the rafters straight. It's a good thing I don't"jump" into projects too quick, otherwise that would have been a big mistake.

I do have a bit of a problem I cant seem to figure out. My plan is to blow cellulose into my attic, and provide airflow via a new ridge vent and soffit vents. But I am not 100% sure on how much airflow I need to provide from my soffit vents to keep the cellulose dry. Here is what I have figured out:

I read through the 2006 International Building Code and briefly through the Connecticut 2005 Building code addendum. These are the only things I found regarding soffit vents/ridgevents:

#1 The ratio regarding (airflow) to (attic area) of 1:300 with a vapor barrier or 1:150 without a vapor barrier. I plan on just blowing in cellulose (no vapor barrier), Here are my calculations:
Attic Area: 1140sq.ft (~26x40ft + a 100 extra)
NFVA for my attic: (1140ft x 12in/
#2 Something saying Ventilation should be balanced as close to 50% at the top of the roof and 50% at the bottom. I plan on installing this ridge vent, which provides 13.5 NFVA per ft. Installed on my home that would provide about NFVA (36ft x

That would provide almost 5x the NFVA that I need. This was one of the lowest NFVA ridge vents I found. I don't think the extra airflow will "hurt" anything, but I have no way of knowing this. So thats my first problem, my second problem. If I am supposed to balance the airflow 50/50 from the ridge to the soffit, I would have to cute some seriously big holes in the birdblocks... And now that I know what their purpose is, I'm not sure what sort of opening to make in them. I would ideally like to screen the opening so no bugs go in the attic, as a small portion of the attic is used for storage.

Any thoughts? Thanks for your time in advance
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post #11 of 12 Old 12-28-2008, 12:35 AM
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Well it will be somewhat difficult to apply the typical screen on the inside of the bird blocks but fyi rolls of screen for that purpose are available in 50 foot rolls by 6 inches wide. I normally install the screen prior to interior finish out ie:sheetrock etc. the screen can certainly be applied exterior of the bird blocks and covered with some esthetically pleasing decoration if you please. Again as in the previous post if there is not space at the top of the bird blocks designed to allow for air flow (I assume you checked although you didn't indicate either way) you may drill a series of holes to allow the air to flow. I don't think there is much danger in getting too much ventilation given your scenario and note that ridge vents do not have to be installed on the entire length of the ridge. Also know that gable venting is also an option and they are available in a veriety of sizes. One thing to consider also is the existance of any hinderence to the ridge opening in the way of blocking. Check to see if there is any blocking at the ridge or other obstruction that would restrict air flow prior to committing your self to the ridge vent.

Of course the whole purpose of this venting is to keep your attic cold and eliminate warm moist air from condensing on the underside of the roof surface or other places with in the celulose rich environment and reduce the chances of mold occurance. The cold roof also will decrease the chances of ice dams which occur right above the exterior walls where the least insulation and the most thermal loses happen. I have installed 2 inch ridgid foam at the eaves to serve as baffles for the air ventilation and add some extra insulative value in the area, filling up undernieth the foam with the blown in celulose. The ridgid foam cut tight to fit between the rafters serves well in this capacity. You can email me directly if you have other questions. I will PM you with my address.

Last edited by mics_54; 12-28-2008 at 12:56 AM.
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post #12 of 12 Old 12-28-2008, 01:14 AM
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BTW the ratio that you need for ventilation being 1:150 for 1040 ssqft of attic would be 1040sqft / 150= 6.93 sqft or 998 sq. in. This mean you need two gable vents (one on each gable) equal to 1/2 that amount...or a ridge vent equal to that amount. The vent holes or spaces in the eves should also equal that number. If your eves are 40' long that is 480 inches of length x 2 = 960 inches. If you had a 1 inch space the entire length of the eave that should be good. A gable vent 22.5 inches wide by 24 inches tall on each gable just under the ridge would be adiquate.
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