The HTRC

The Homeowners & Trades Resource Center

Brought to you by:

You are here: Home / Common Sense Building / Getting the details right: Door & window openings (interior)

Getting the details right: Door & window openings (interior)

When buying new doors & windows (for either new or remodeling) most manufacturers generally require a rough opening size 1/2″ larger than the actual unit size. This requirement is just in case things are not perfectly square or plumb. So how should one finish it off after the unit is installed (fiberglass / foam/ who cares), what happens if the opening is oversized, what about caulking the trim afterwards?

Make sure the unit is centered:

When installing a door in an opening one should make sure it is solidly on the (sub)floor / slab and centered in the opening. When installing a window it should be completely centered in the opening which most accomplish by using shims temporarily at the bottom. Why is this so important? That is so that one can install foam around the unit to not only act as a thermal break but also to help prevent air-leakage (which also means moisture).

What happens if the opening is larger than 1/4″ to 1/2″?

an-inch-gap-ouch

Believe it or not, that is what I found behind the trim in my place – a one plus inch wide gap on both sides (oh and a mouse skeleton looking at me). I know many carpenters that would automatically fill that gap in with a 3/4″ board thus getting down the 1/4″ to 1/2″ gap but guess what – it isn’t always necessary. Fortunately the trim outside easily covered the sheathing and it was shimmed in adequately (well when I finished it was).

So what happens if the gap is to large – well as mentioned above you can always add in a 1x or 2x depending on the gap. Personally if you need to add in a 2x you might want to consider a 1x with a 3/4″ or larger piece of foam – don’t forget about taking care of the sheathing & wrap/flashing details outside.

How shouldn’t you fill the gap?

dont-use-not-code-compliantLet me first start with these two pictures that you shouldn’t see… Back in the 80’s maybe, by the early to mid 2000’s most everyone was learning better. Still seeing it in displays within the last few weeks… ridiculous. Yes we are talking about fiberglass.

As an FYI – The picture above is from the 2013 Remodeling Show but they still are using the same displays this year. Another quick point is Anderson Windows specifically call out for foam to be used, not fiberglass – anything like do as we say not as we do? 🙂 As a reminder – since the 2006 IRC one cannot use fiberglass as an air barrier material as shown in this piece highlighting the IRC 1102.4.2 table

How do we deal with the gap?

fill-gaps-properlyPer the codes (in this case the 2015 found in 4.1.1) “The space between window/door jambs and framing, and skylights and framing shall be sealed” & “Air-permeable insulation shall not be used as a sealing material.” In this case the answer is pretty simple – you can only use foam & it should be low expansion. Why not fire-rated, or regular foams? The answer is pretty simple – it can take up to a week to cure / fully expand and is known to deform door jambs & windows preventing them from working right.

But wait, can’t I use fiberglass & “seal” the gap with caulk? Technically you could, assuming you can find a manufacturer that will warranty it and an inspector that would pass it. With that – for windows that have an extension jamb or drywall return, I would encourage you to run a bead of caulk between the window, framing & where the drywall / extension jamb meet.

Caulk & Trim Work:

It used to be the most popular mantra* out there – to save energy caulk around the windows & doors… Unfortunately while the advice is good, it is wrong as the caulking you need to really be worried about is on the exterior & not the interior. It really doesn’t do you much good if you allow cold air to short circuit the insulation.

With that as a builder & a remodeler, the trim should always be caulked (yes even on interior doors.) Why? Well because not only does it look better, but it also allows the paint to adhere better. With that said, while the mantra is getting a beating – if you see air moving curtains / feel a draft in the middle of winter it can definitely help your comfort levels & hey it just might save you a little bit. Just don’t forget to head outside in the spring to solve the real issue which probably includes water leakage.

* Many have been stating for a while that caulking around doors & windows / checking weather stripping isn’t as important as you might have been led to believe. For more on that check out Energy Vanguard’s latest post (and comments) “Winterizing your Home? Don’t caulk the windows” or our piece on FAQ: Are all air leaks equal?

Related posts:

FAQ: Do I need to change my HVAC filter monthly?
Utilizing Universal Design Principles to create an Accessible Deck
Insulation Requirements & 2021 IECC First Look
FAQ: Should I always use the Bathroom Fan when taking a Shower?
Gas vs Diesel vs Electric: Trucks, SUV's, Towing & Camping
Industry Standards 101
BS4D: Building Codes
FAQ - Do I need storm doors or windows?
  Tweet    
  
   

Filed Under: Common Sense Building, FAQ's, Acronym’s, & Terminology October 23, 2015 By SLS

Comments

  1. EnergyVanguard says

    October 23, 2015 at 09:10

    Nice article, Sean. And thanks for the mention and link!

    • SLS Construction says

      October 24, 2015 at 06:02

      Thank you very much Allison & my pleasure – besides, I couldn’t leave it out as it was what kick started this piece a few days back
      Thanks again & I hope you are having a great one

  2. Greg sureseal says

    September 12, 2021 at 09:17

    These door and window openings details are breathtaking, and I will use these details in one of my new projects. I am thankful to the writers for sharing this excellent article here.

Featured Posts
Hurricane Season – 5 Steps to being prepared

Hurricane Season - 5 Steps to being prepared

Today is the start of Hurricane Season that has been predicted to be busier than usual. Based on the ocean temperatures and the changing weather conditions, they might just be ...

Read More

August and Late Summer Maintenance Checklist

August and Late Summer Maintenance Checklist

Well I have some good news & some bad news – the good news is that this is the last full month of summer. The bad news is that it ...

Read More

25 ways to keep your cool during a heat wave & beyond

25 ways to keep your cool during a heat wave & beyond

Welcome to the dog days of summer with what appears to be a bumper crop of “Excessive Heat Warnings” this year. In just this last week, I got to enjoy ...

Read More

Hitting the Road: RV’s, Gas Mileage, & Assorted Tips

Hitting the Road: RV’s, Gas Mileage, & Assorted Tips

As the Star Trek transporter still has not been invented, many vacationing families & others start looking to RV’s due to their many benefits. Can one say no TSA checks, ...

Read More

FAQ: Do I need to change my HVAC filter monthly?

FAQ: Do I need to change my HVAC filter monthly?

If you follow our Monthly Maintenance Program, the first item we have listed is "Change out your HVAC filter." This has brought up a few questions, namely: Do I need ...

Read More

Back to School Organizational Tips

Back to School Organizational Tips

Ahhh, back to school time - maybe I can now get a little peace & some quite time, get some things caught up - truly, this is one of the ...

Read More

FAQ: Ceiling fan direction - summer & winter

One of the biggest questions out there is which direction should my fan be running and how can I tell. You look at the switch and realize it isn't any ...

Read More

Subscribe

Get new posts by email:

Random Glossary term

  • Capillary Action

    When buying new doors & windows (for either new or remodeling) most manufacturers generally require a rough opening size 1/2″ larger than the actual unit size. This requirement is just in case things are not perfectly square or plumb. So how should one finish it off after the unit is installed (fiberglass / foam/ who […]

The HTRC - Copyright © 2006–2022 by TheHTRC.com & SLS Construction & Building Solutions LLC http://SLS-Construction.com