Building Decks Right Around Basement Windows


It is not unusual for a houses’ basement window to be facing the backyard, an area also ideally suited for a deck. Raising the questions about decks around basement windows. Also related is decks over a basement window. These common questions around decks and windows we are going to address.

Deck openings around windows need to be reinforced to support the additional load as the joist by the window cannot be supported by the ledge. Also, the risk from falling into the window well needs to be minimized by a grate or deck guard railing preventing falls.

Let’s start with the framing for the opening for a basement window and then look at the safety concerns.

Framing around a basement window

The challenge with framing a deck around a basement window is the missing section of the ledger where the window is. This section of ledger needs to be replaced with a flush beam, hangered off reinforce joist, also acting as flush beams. The level of reinforcement depends on the size of the opening, the more joist and deck that needs to be supported, the more reinforcement needed.

Deck opening framing for a window

  1. Double up the trimmer joist of the header joist. I like to keep the trimmer joist back at least 6″ (150mm) from the edge of the ledger providing a stronger connection.
  2. Joist header
    1. Deck opening less than 4′ (1.2m), a single header can be used.
    1. Connect the trimmer, header and header joist with approved header joist.
  3. Connect the trimmer, header and header joist with approved header joist.
  4. Install blocks between the header joist and ledger to clean up the window box and hide the hanger from view.

There are a few safety concerns with building a deck around a basement window. Both from inside and outside. How we address these differ between egress and non-egress window.

Sunlight entering the window, that’s a good thing

I developed basements for many years, and few things improved the feel of a basement as a window. If your basement has a window you don’t want to board over it, close it in. The more light entering your basement, the better. Of course, a deck and the existing window well limits the view already, but the sunlight is the essential element.

Therefore, you want to build the deck in a way that light can still get into the basement. Far enough away that the sun can shine into the window well and window.

Equally important is fall risk

A ground-level deck framed around a basement window may be considered a ground-level deck around the deck’s perimeter, but the depth of the window well will increase the fall risk.  Not unusual for a window well to be 24″ (0’6m) below grade. Therefore, a deck 24″ (0.6m) above the yard fall into the window well is 48″ (1.2m). Not good, not good at all.

There are two solutions depending on if the window is an egress window or not.

What is your basement window?

The easiest way to know is if the window is for a bedroom, it is an egress window. There are many little determining factors, but if the window will be used for escape in a fire, it’s an egress window. The deck must be built in a way to allow whoever is sleeping down there to escape.

Before discussing codes and law related to window egress safety and your deck, I want to make something crystal clear. Regardless of code, rules and laws, you want your child or yourself to be able to escape in the event of a fire safely. This is the more important question when building a deck around a bedroom window. Can they easily escape? Remember a fire is an emergency, clear thoughts are far from us and panic is controlling. Escape needs to be simple and easy. Everything done around an egress window needs to aid this. If after building the deck and escape is not easy, change your deck and plan. Safely of your love ones is the driving factor not, “does it meet the minimum code?”

Non-egress basement window

For a non-egress window, a grate or transparent cover is a great solution. Strong enough to be walked on and not detract from the deck. Being removable is also a good idea. Allowing you to clean the window or if something falls into the well, you can get it out.

The metal grate reinforced strong enough for the required span. Often being greater than 24″ (0.6m) to allow sufficient light into the window. The most economical solution is a basic grate, but you can also embrace the look with a little more flair in the metalwork design. It will cost a bit more but may complement your deck more.

Egress basement window

An egress window, we are more limited. Jurisdiction varies, but here are the rules for Calgary where I build decks are.

“4. Covers or grates over a window well serving a bedroom are not permitted unless reviewed and approved on a case by case basis.”

City of CalgaryOpens in a new tab.

Yes, you could seek individual approval. My experience, if you are not a large builder individual exception, which is what you are asking for are rare. You could apply for the permit with a grate and see how good your negotiation skills are. Knowing that, if you fail, then you will go with the second and code meeting option.

Railing with a gate around the deck opening.

Yes, a gate is required for escape. The railing around the window needs to have an out-swinging gate. Allowing easy exit through the window and out of the window well. The gate facing towards the yard providing a clear path from the out of the window to the yard.

Railing does limit your deck but doesn’t have to be ugly. Railing matching the rest of the deck blend in nicely and can even enhance the look of the deck.

Since we are discussing decks and basement windows, what building a deck over a window.

Can you build a deck over a basement window?

Short answer Yes, you can build a deck over a basement window. Depending on the height and size of the deck, it will impact your basement. A deck over a window will shade the window, limiting basement sunlight. A higher deck over a walkout basement window projecting less than 12′ (3.6m) will shade the window but impede the view very little.

As we just discussed with building a deck around a basement window, building a deck over a window also depends if it’s an egress window or not.

Requirements for egress windows under a deck.

Safety is our number one concern. God forbid, but in the event of a fire, you must be able to escape the fire through your window and not get trapped under the deck after climbing out of the basement. The rules about egress windows under decks will vary by jurisdictions, but let’s go through the city of Calgary’s rules as an example.

“Egress windows below decks are not permitted unless there is a minimum headroom clearance of 2.1m between grade and the underside of deck, or there is a minimum headroom clearance of 760mm between grade and the underside of deck and the window opening is immediately adjacent to the edge of the deck above.”

City of CalgaryOpens in a new tab.

Which primarily limiting decks over egress windows to walkout basements. To meet the 2.1m (7′) distance between grade and the underside of the deck with most attached decks slightly below the main floor height.

The exception being if the window is “immediately adjacent to the edge of the deck above.” Then the underside of the deck only needs to be 760mm (30″) above grade. But what is “immediately adjacent” not being clearly defined in this sentence? Further down in the guidelines egress window under cantilever are limited to cantilevers 610 mm (24″) or less.

“5. Egress windows below cantilevers shall have a minimum clearance of 760mm between the underside of the projection and the top of the window well or adjacent grade. The cantilever should not project more than 610mm from the principal wall.”

City of COpens in a new tab.algary

I think this can also be applied to egress window below decks. If the window is less than 610 mm (24″) from the edge of the deck, it will work for egress. Any greater than two feet, and it’s no longer safe as an egress window.

A basement window doesn’t prevent a backyard deck, but it will take a few extra steps. Build it right, build it safe and enjoy your deck.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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