Transforming attic window into attic vent

Blog entry by Obernelson posted 09-30-2010 03:10 PM 19685 reads 0 times favorited 5 comments Add to Favorites Watch

I have been on LumberJocks for awhile and when the CreativeHands News came out I noticed the HR Create and Share Challange – Windows Wonders, and having just completed the window replacement with a vent I figured I would share the experience.

The window conversion project revolved around a house built in 1793 and in a need of some new roof rafters, roof boards, new shingles and attic ventilation. The contractor doing the work told me that he would put in custom soffit vents in for air circulation to eliminate ice dams that have been occurring for years but I needed to decide a way to exhaust the air.

The problem was that the 5 sided ridge beam would not allow a common ridge vent system, so he recommended power vents. Not wanting a powered system I decided to go with a passive vent system. We looked to the attic window that was used for letting light in only, and since the attic wasn’t a functional space the decision was made to use it as our vent location.

This decision was made on the fly and it became my job to build a vent as the alternatives the contractor offered was he could get an off the shelf vent at no cost or he could hire a carpenter to make a custom built vent to fit the spot. Not wanting to have an off the shelf vent put in and look like it didn’t belong or have a significant cost overrun having a contractor do the work I decided to build my own vent.

I designed the vent to fit against the existing window stops, but the problem was that the new roof was on and the access from the house was limited to a small access hole, and the thickness of the vent due to the pitch and length of the louvers would not fit through the window hole or the access hole.

After some quick prototype builds of the louvers the design consisted of a frame around the louvers that would fit through the attic hatch and an exterior frame that would be added in the attic. Then a face frame on this that finished the look and would rest against the original window stop. Inside the attic the finished vent got a common door screen to keep out bugs and a ¼” wire mesh was placed on the inside of that to keep unwanted critters out.

This picture shows what he attic looked like with the window and before the vent was installed.

The final result was a functional vent. This picture shows the new vent installed and before final painting work done.

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5 comments so far

View Obernelson's profile


3 posts in 3030 days

posted 09-30-2010 03:13 PM

First post on the forum and was learning so here is a picture of the final roof and the soffit vents being put in.

View MsDebbieP's profile


628 posts in 3954 days

posted 10-02-2010 11:54 AM

you people are amazing ….impressive.

well done!

-- ~ Debbie, Ontario Canada

View dustygirl's profile


321 posts in 3728 days

posted 10-02-2010 03:55 PM

Your new vent looks good.I like the well thought out way that you constructed it.

-- Dustygirl Hastings,Ont. Life is too short to sit around doing nothing

View Obernelson's profile


3 posts in 3030 days

posted 10-04-2010 11:14 PM

Thanks for the views and comments.

I figured I would post a few comments to those that may be interested in building a custom vent. I started this project with little to no research opting for the learn by trial and error method as I was put under some pressure to get this done while the contractor was there.

On the technical side I used a Sears portable job saw, 3/4 PT plywood for the outer frame and 3/4 pine for the louvers and face frame. The project does not require extreme accuracy.

The notch for each louver on the inner frame were done with repetitive passes with the table saw stepping blade width for each cut. I could have set up a dado blade but the project just didn’t need that level of detail and I as only making one vent.

When doing my prototype of the project I learned that the inner frame rails with the notches should be kept longer than needed to allow for the miter on the saw to be used on one side for all passes or you would have to switch sides and continue cutting as your cuts would end up near the end of where you push with your miter gage and would loose control of the material as you push. When done you can cut the sides to length.

The window frame I was putting the vent in had about a 5 deg pitch to the window sill and I used the same process that replacement window installers use that with less than 8 degrees just caulk the crack under the bottom frame to make a good seal. This saves adding a step to angle the bottom of the frame to match the window sill pitch.

If you don’t end up with the right amount of space top to bottom so you have even spacing between the louver slats it seems to work fine to cut the bottom and top short of full size but do not cut the bottom slat short as this is your drip edge for the louver. Take the rest from the top down leaving the bottom slat sitting on the bottom of the inside frame.

The louver slat width were sized to fit exactly edge to edge on the inside of the frame to the outside of the face frame. The width of the inside frame needs to be wide enough to ensure the proper overlap of the louver slats so rain does not get in. Mine was sized to fit the window frame in the attic allowing a small stop to be put on either side to prevent movement. I used 45 degrees for my louver angle and this seemed to work fine and is easily done on a job saw without any special setup.

All inner frame and face frame received primer and exterior paint before assembly as painting between the louvers later was not a practical solution. Then the assembly of the inner frame and louvers was done with glue and 18 ga. brad nailer.

I did not install a face frame board to the bottom as I didn’t want the face to sit even or proud of the bottom slat drip edge. This worked fine in that there is no window stop on the bottom that you meet up against anyway.

I have a portable air tank that I fill from my compressor so I can make my brad nailer portable to the attic. Final assembly was done in the attic with a final coat of exterior pint before installing it against the window stops.

Once the vent was installed the fiberglass window screen was added then the ¼” galvanized wire mesh over the screen.

The project uses a number of basic woodworking skills and although you may go through some lumber to build a prototype it was well worth the effort to save the cost of having a custom vent made and the time it would have taken to make.

I used a few hours of one day to work on the prototype and decide the size and angle that would work best. I then quickly cut the slats and side frame pieces. The next day I spent a few more hours making the exterior and face frames and applied the primer and exterior paint to all parts. The third day was a few more hours to build the inside frame and take all parts to the attic and complete the assembly and put a final coat of paint on the vent and painted the window frame and window sill. After these dried I installed the vent and applied the screens. In all I would estimate this to be about a 10 hr job if you have never made one or had a plan. It would be half this time if I was to ever build a second.

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628 posts in 3954 days

posted 10-04-2010 11:18 PM

wow. Thank you so much for sharing the “how to”.
I love our sites and members – so helpful!

-- ~ Debbie, Ontario Canada

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