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Ensuring your SIPs Window Rough Outs are Correct

Started by jb9, November 03, 2017, 08:28:15 PM

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I am going to be enclosing my timber frame with SIPs and I get a little anxious about the mistake where the panel fabricator puts the window rough outs in the wrong spot.  I have heard of some guys doing site cuts on the panels...  Anyhow, I had an idea for a technique that I think would be easy and effective.  I wanted to run it by some of the pro's here.  Anyhow, here's the idea:

Build 2 identical jigs (or square frames) the size of the RO and "hang" them off a pair of corner dowels or screws drilled through the panel.  If the dowels were parallel and level, I would think the frames would be in the correct position against the OSB.  Then all you'd have to do is scribe the lines against the OSB and make clean plunge cuts.  I don't have a frame/enclosure design with a multitude of window sizes, but I think this might really give one the confidence to keep the windows away from the braces.

I have attached a rendering of my idea.  I agree that it would require fabrication of the jigs but I think it might be worth the piece of mind and perhaps the reduced cost of the window cuts by the manufacturer.

Any thoughts from pro's or finish carpenters are welcome.



How bout filling out your profile so we'll know where you are, etc.  I promise no junk mail.  Just well-intended if often wrong advice.

Not the pro you pleaded for, but as a non-every-day amateur at building, esp wood framing style using our glorious site milled timber, I like anything that gives more certainty.

Your idea looks good.  I have heard bad stories about letting the sip mfr do the cuts, and they charge a fair amount for doing so.  I also know from installing windows in conventional construction that t&s (trims n shims) can fix a fair % of mistakes.  Made a few, I have.

I'm guessing the SIP maker errors are a higher level of magnitude than most made on site.  Totally wrong wall, etc.

And the fact is the longer you can wait before cutting those holes, the greater the chance that you or your spouse will have made his or her last change in the window/door plan.

For the pins use big n heavy 10 or 12 inch timberlock or similar screws.  No pre-drilling required, esp with OSB and EPS.  Easy re-use.  Start em into the OSB and then do your level plumb n square final checks on them before going in farther.  If you mess up, the sheetrock will cover the holes, and you can start over.

I cannot see why you need a jig.  Just snap chalk lines using the corner screws.  Use your schedule of windows and doors by size to make out the proposed rough size for each one so you can locate-mark, locate-mark, locate-mark, then cut (or have your helper follow along and cut) until you are done.

I have seen chain saw type adapters for classic Skill 77 and similar saws (worm drive--stronger that most ordinary circular saws) on Amazon for around $150.  I would think you'd then have what you need for plunging in where less out of the box thinkers would fear to cut.

Or...They saw not what you wood?

In fact I have seen such adapters on job sites involving SIPs recently.

Do my suggestions make sense?  I don't have a smidgen of the hands-on experience some of these guys do, but sometimes that can be an asset.

It seems like the freedom allowed by timber framing's "wide open spaces" should make putting in the windows & doors easier, but I'll find out, won't I? (really)


Thanks MbfVA.  The other advantage to this method would be that once the panels were installed, the structure would essentially be at the "dry-in" stage.  You could pull a window off of a stack (neatly stored inside), cut the RO using the method described and subsequently install the window.

Arguably, the structure would always be at "dry-in" even if this 2-step process took longer.

Additionally, this technique would require a "hot knife" that the SIP manufacturers use to cut out a cavity at the edge of a panel for dimensional lumber (e.g. a soleplate or a header or a sill).


Interesting, would the hot knife also be what you would use for cutting the channels for splines between panels, or would my chainsaw helper be more applicable for that?

By the way,  no SIP manufacturer that I have spoken with has mentioned those splines.  I learned about them from a prospective tenant, a carpenter, who called about one of our rental properties.  We got into a discussion of timber framing & sips.   This guy used 2x6s.

I wonder if there is any thermal bridging affect from doing that. (really)


When I do the sips I almost always cut them onsite.  I just lay out the door and window opening on one side and drill thru the corners to get the other side.  I cut both sides with just a 7 1/4 saw and saw the remaining foam with a hand saw.  Use a foam scoop to remove the foam from the window buck and nail or screw the 2x in after putting expanding foam down.  Foam scoops are less than 200.00.  No big deal if the osb isn't even on both sides, just level and plumb the 2x.  I usually use osb splines between the panels and foam the heck out of the 2 panels before pushing them together.  Some panel companies use caulk instead of foam and I'm not sold on that yet.  If everything is perfect it works great but most panels aren't perfect and I can see where places may not be sealed.  I will use expanding foam until convinced otherwise.
LT40HD, 12' ext, 5105 JD tractor, Genie GTH5519 telehandler
M&K Timber Works


Thanks logman.  I just got back from the woodworking store and was looking at routers with plunge bits.  It seems that as long as the location on both sides is properly located (my idea showing the hole drilled at a couple corners), this seems like a task that can be accomplished.  I appreciate hearing your thoughts as a pro.  Do you try and cut them flat or can you make that plunge cut with the skil saw when the SIPs are installed and vertical?

For cutting so far, I have heard the following:

-Skil Saw (7 1/4" blade)
-Skil Saw with 14" bar attachment
-Jig Saw with fence

I'll have to see what tool might work for me.

I will definitely have to pick up the foam scoop.  Thanks for the tip on foam vs. caulk too.


Usually when the sips are up.  I have a Prazi saw attachment but really never used it much.  A battery powered circular saw is easier to work with if the sips are installed. 
LT40HD, 12' ext, 5105 JD tractor, Genie GTH5519 telehandler
M&K Timber Works

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