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new construction window install: q. about shims and expansion

Posted by tom248 (My Page) on
Mon, Oct 31, 11 at 12:29

I am in the process of installing new construction windows (Andersen 400 Tilt&Wash Double Hung), and have a question about the installation.

The installation instructions say to shim the sides at top, middle and bottom. Fine, I can do this. I believe this is to prevent bowing of the windows. But I wonder, what about expansion/contraction? How will expansion/contraction occur when the sides are shimed in three places? Won't the shim interfere with the normal expansion/contraction of the windows within the rough openning? The windows I am replacing are 30 year old wood windows and they were not shim'ed at all on the sides.

Sorry if this is a silly question. And I have no problem following the recommended install instructions. But I just can't get past the expansion issue when the shims are concerned.


Follow-Up Postings:

RE: new construction window install: q. about shims and expansion

I will start by saying expansion and contraction on the windows installed in a home is less of an issue than windows not properly shimmed to keep the jambs straight. I would make certain the units are properly shimmed per the manufacturer.

RE: new construction window install: q. about shims and expansion

Wood does not change length appreciably with moisture content.

It changes width and thickness in a typical piece.

The windows do not need any room top expand in the rough opening.

RE: new construction window install: q. about shims and expansion

Installed properly, you should not have any issues.

Proper shims and spray foam are your best tools in this application.

RE: new construction window install: q. about shims and expansion

thanks everyone for the replies and assurance i was not missing something. I guess the 1/2" extra dimensions in the rough openning to window size spec is to allow for the rough openning to be 'rough' and therefore not as precisely square as the window, as well as to allow for sealing (with insulation or foam, i'm intending to use mostly foam).

I guess after installing hardwood floors throughout my home over the past year, i've been so focused on the expansion gap necessary at the walls, that not having space for the expansion in the windows seemed strange. However, flooring of course has a lot more wood surface from which to expand.

thanks again.

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