How to Install a Window in New Construction

A how to guide for first time installers to put a window into new construction

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Table of Contents

One of the first big projects I recommend to new homeowners, other than fixing their own toilet, is actually learning how to install a window. It’s a project that makes complete sense with how to put it together.

Learning how to install a window scares people needlessly. What frightens people the most is that they won’t know what to do. But that’s why I’m here.

Basic Thought Process To Install A Window

To start learning how to install a window, you need to think like a water drop. Water flows down with gravity. Because of this, you need to put your layers on from the bottom to the top so layers overlap.

When you install a window, you are basically putting up defenses against water. From the butyl tape to the housewrap, everything is just keeping water from getting behind the water and into the wall.

If you think like a water drop, you will install a window perfectly every time.

Framing To Install A New Window

Basic Wall Framing

A wall is made of studs running vertically throughout the wall. These studs are usually made of 2×4 or 2×6 Douglas Fir lumber. The studs are connected to a sill on the bottom and usually a double top plate on the top.

Studs typically are 16″ apart on an exterior wall. Actually, many interior walls are also built with studs of the same spacing but they are allowed up to 24″ apart.

The distance is a measurement called “on center.” This means that the measurement is taken from the center of one stud to the center of the next stud.

Framing Around A Window

When a window is framed in, it is vital that there are two studs on either side of it that go from the sill to the top plate. These are important for structural support and to keep the wall from sagging.

The window sits on a support going horizontally across the opening. You cut the studs in the wall to the height at the bottom of the window and connect a support piece across between the studs going from bottom to top.

The important thing is to remember that the top of the opening needs to be supported. A horizontal piece of wood across the top of the opening is supported with studs that go to the bottom sill. The wider the opening, the thicker the top support needs to be.

What Size Do You Make The Opening For A Window?

When you are framing to install a window, you want to make the final rough opening roughly 1/2″ larger than the actual window measurement. The rough opening is the gap between the studs and the top and bottom pieces.

Most window manufacturers actually account for this and they make their windows to fit openings that are full foot sizes. So they make openings to fit 3′ x 3′ instead of making the framer use partial inches.

How Do I Measure For A New Window?

If you are measuring your opening to prepare to go to the hardware store, you need to be able to communicate how and what you measured. There are 3 main measurements for windows:

Rough Opening: This is the opening/space between the framing members. This is the most common way to define a window size when ordering.

Call Size: This is actually the same as a rough opening. If you need a window for a 2′ x 4′ rough opening, you need a window that is called 2×4 even though it measures smaller.

Net Size: Net size is 1/2″ smaller in either direction than the rough opening. So the net size of a 2×4 window is 1’11-1/2″ x 3’11-1/2″. This is the second most common method of measuring for a window to order.

Final Steps To Frame For A New Window

Make sure once you have all of your framing put in, make sure to inspect it to make sure that it is relatively square and clean. For more details on how to frame to install a new window or door, check out the this series on shed building.

Install A Window Step By Step

Cut Into The Housewrap

Cut the house wrap that covers the window opening in an X pattern. I know that you may be tempted to cut off the spare flaps but don’t do it. Instead, you will use the flaps as extra waterproofing layers.

The bottom and side flaps should be wrapped into the window opening and stapled to the inside of the framing of the interior wall. The top flap needs to be lifted up and taped to the outside of the wall.

Install Flex Wrap

Once your housewrap is hooked up correctly, you need to protect the bottom sill of the framing. An old way of doing this is to cover the bottom sill in butyl tape and wrap the tape up the sides of the framing.

Instead, I highly suggest you use Tyvek Flexwrap. This is a stunning product that actually flexes around the corners where the bottom sill meets that side framing. That way there isn’t any chance for dry rot or water damage in the bottom corners.

You apply the Flexwrap by peeling off the backing paper and setting it on the bottom sill. You need to make sure that the Flexwrap will wrap up the side sills by 6″ on each side. Once the Flexwrap is stuck down, make sure to press it on using a J Roller since the adhesive is pressure activated.


You should know that the Flexwrap will stick to anything so be careful. Not only will it stick to itself but it will also stick to the side of the house, the floor, whatever you put it on. You have one shot to get it in the right spot.

Insert and Fasten Window

Set the window into the framing and use either roofing nails or truss head screws to fasten it through the fins on the sides. These two types of fasteners are flat on the back so they allow the window to move up and down with the structure and keeps the window working longer. Never use a countersunk fastener to attach a window or the window will bind in the framing.

The other important factor is to never fasten the window on all 4 sides. If you do that, the window cannot move as the structure moves and it will bind. I am a firm believer in fastening only the sides of a window but I’ve had many spirited arguments with contractors who swear you have to fasten the top or bottom as well. However, the windows I’ve put in don’t have these extra fastners and they have yet to fall out of the house.

Apply Blueskin Around Window

Blueskin Steps

Blueskin is a brand of butyl tape, though any brand can do. This sticky tape is usually 4″ or 6″ wide and it covers the fins of the window and sticks to the framing. It serves as another layer of water protection if applied correctly. The side pieces are applied first, overlapping the bottom flex wrap and extending above the window by 6″. The top piece is applied last and it also overlaps the side pieces of blueskin.

Final Waterproofing

Apply a drip edge flashing to the top of the window above the blueskin. The drip edge will help rain water to fall off the face of the window rather than potentially following surface tension behind the window. The drip edge can be attached with the same fasteners as the window itself. At this point, fold down the flap in the housewrap and tape down with another layer of blueskin, making sure to tape all of the cuts.


So, your window is installed completely. You only need to install the trim around the outside of the window to finish it off and make it look pretty. If you need more information on choosing an exterior trim head over to this post. On second thought, maybe add a window box to the bottom of it to really make it look nice. It wasn’t nearly as hard as you probably imagined either, right?

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Head Homeowner

Hey everybody! I'm Sydney, the head homeowner here. Let me know if you have any questions you didn't find the answer to. Tell me what projects you're working on. I love to hear from all my readers.