Building Soffit Boxes (And wood soffit installation.)

I equate soffit building (particularly those funky boxes on the corners) as the house-building equivalent of being attacked by a shark. One minute you’re all swimming along, soaking up the rays, thinking how easy it will be to install siding (a two or three weekend job, right?)– things are going well for you. And the next thing you know you’re missing a foot, flailing helplessly, hoping someone (I’m looking at you, Google) will be able to rescue you, and wondering what the hell just happened to your life, plans for siding the house, peaceful day at the beach.

Another thing soffits and sharks have in common? Never saw it coming.

Soffits were just something we were going to worry about later, and the next thing you know we’re trying to put siding on and realize that 1.) The soffits have to be up to put the corner pieces in place, 2.) The corners need to be in place to put the siding up, and 3.) We have no idea how to build the soffit boxes.

This is the age of Google and YouTube after all, you think someone would have a damn tutorial on how to put a wood soffit box in, but no. So we had to go back to the age-old method of faking our way through the entire process, but as it turns out we’re pretty good at that once we’re done flipping out about it.



Let’s talk specifics, shall we?

Soffit Installation

Everything about this general area of the house– drip edge, fascia, soffits, etc– was a bit of a mystery to me. I’d thought about the roof shingles, the windows, the doors, the siding, but who the heck plans our their soffits ahead of time? (Probably professionals, actually.)

Every time I took a picture of what we were doing MysteryMan was all, “You know there is no way in hell we’re doing this the right way, right? You shouldn’t be showing this to people.” But I’m not an engineer, which means my one qualification for if we’ve done something the “right way” is this: Did it work?

Answer: Yes.

Okay then.

Step 1- Blocking

For all the soffits we started with blocking. MysteryMan did all sorts of complex measuring (which for me translates to holding up a level) to make sure the blocking was in straight.


The purpose, of course, was to give us something to nail the trim to.

Step 2- Soffits
The soffits on the flat part of the roof (parallel to the ground) need vents to keep air circulating through the attic so you don’t die of The Mold. I’ve seen this done a number of different ways, but this is how we did it.

We used 1/4″ exterior grade plywood ripped down to the necessary width. (Both sides primed, bottom side painted.)

To properly install the vent we first put up a 3″ piece of wood with staples…

02_outside piece

The vent has a 1/4″ lip on either edge to keep in in place (so don’t staple any of your wood up within a quarter-inch of where the vent goes).


We pre-painted it, then slid one side of the lip under the first piece of wood, and installed the second piece of wood on the other side.


It’s not rocket science, but it did take us a little bit of time to get there.

Any peaks were done with just ply ripped to length and stapled in place (no vents).


This part did not particularly require Google, but to get there we had to build the soffit boxes, and that, my friends, was a right pain in the ass.

Building Soffit Boxes

I was busy moving five years of my life out of my old house during this adventure, so full credit goes to MysteryMan for doing this without my help.

Step 1 – Frame

He started with a “frame”. This was a three piece wood box that consisted of a triangle piece, a back piece, and a small nailer to attach the whole thing to the house.



Step 2- Trim

Then the painted 1x cedar trim was cut to fit, one piece for the “triangle” in front, and once piece for the back. Because of the size of the stock we had, the piece in the back is shorter than the bottom of the traingle piece or fascia, but we preferred using what we had to buying new.


It took some clamps and a little finagling to get the pieces tight.


The outside of the box needed to be complete before we could finish the bottom of the soffits.


And getting the bottom piece to fit just right? Almost impossible. Luckily caulk forgives many sins.

Step 3 – Nub removal

Our soffits hung out like this for a long time, because they were good enough to allow us to move forward with the siding…


For it to really look finished though, we needed to remove the nubs. A perfect job for my Rockwell Sonicrafter.


A little primer and paint, and can we just say, thank god that job is done?

And I know, it doesn’t look that difficult in the pictures. In retrospect we’re like, well, duh*, how else would we do it… but getting there without a diagram, picture, napkin drawing, or otherwise directive, was harder than one might think.

*Just in case there’s any confusion, MysteryMan has probably never uttered the words “well, duh” in his life. I’m pretty sure he thinks them sometimes though.

13 Responses

  1. Great Post. I love seeing “this-is-how-we-did-it. Deal-with-it” posts. I wrote a little bit about all the eave returns in my 100 year-old neighborhood here. And then you can read about my own eave return project here and here.

  2. This is such a great and helpful post. I can relate to it exactly as I am finishing up a massive two story garage undertaking. I hadn’t planned anything for the soffits, hoping YouTube or google would solve my problem. Luckily I was able to find your article. Thanks again, I’m sure you have saved me at least a few hours of frustration.

  3. Thanks you so much for this post! I was really scratching my head yesterday about how to build these soffit boxes. Looked in all the usual places online, DIY books, even drove around the neghborhood staring at other peoples soffits/eaves looking for clues. Your post was EXACTLY what I was looking for!!

  4. Fantastic. I had no clue how to do this until I read the post. Tip..use the factory edge for the part that fits below the fascia board if you want tight fitting edge.

  5. Very helpful, and your right about the lack of info for wood soffit. Thanks for sharing.

  6. Thank you so much for this… Just finished a bump out storage and workshop on my garage and for some reason… Can’t figure this part out. Lol. Just need a simple pork chop and good to go!

  7. Any suggestions on this to look nice on an eave on an gable that flairs out from 24″ to 49″ the top

  8. Kit – I have searched every which way but Sunday for this. I put an addition on our barn…that was the easy part (shop, milking parlor and new indoor/outdoor chicken coop)…now on to the finishing touches and I have been dreading this for weeks, but thanks to you I’ll tackle this weekend!

  9. Hey, So its 8 years later and kfound myself here after searching DIY soffits. Thank you for the cool info and real dish on this and also giving mystery man credit for his PITA job.
    You guys are a true inspiration to many in the USA. Keep it up

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