Sunroom Addition vs. Balcony Glazing in Seattle: Which One Actually Adds Square Footage?

By Ruslan Bencheci, Owner and CEO, Star Construction WA. Washington State licensed contractor #STARCCW791L5, bonded and insured. Bothell, WA. Updated August 2026.

Short answer: a sunroom addition adds square footage to your house. Balcony glazing does not, and it is not supposed to.

That distinction costs people money. I have sat at kitchen tables in Ballard, Magnolia, and Newcastle with homeowners who thought they were buying one thing and were actually pricing the other. Sometimes the gap is forty thousand dollars. Sometimes it is the difference between a project that shows up on an appraisal and one that does not.

So here is the whole thing, laid out the way I explain it on a first visit.

What “square footage” means to an appraiser

When people say square footage, they usually mean the number on the county record or the listing. Appraisers call that gross living area, and it has rules attached.

For a space to count, it generally has to be finished, heated by the same system or an equivalent permanent one, accessible from the rest of the house, and enclosed by permanent walls. It also has to be above grade, which is why a beautifully finished basement in Wallingford does not get counted the same way as the floor above it.

The word doing the work there is permanent. A room you can slide open in July is not permanently enclosed. That is the entire reason a Lumon balcony enclosure and a sunroom addition land in different columns.

I am not an appraiser, and appraisers do exercise judgment. If your project hinges on the square footage number, call one before you sign a contract, not after. It is a cheap phone call.

The three things people call a sunroom

Almost every job I quote falls into one of these. They get lumped together online, which is where the confusion starts.

Balcony or deck glazing

Frameless retractable glass panels that slide open and stack to one side. We install Lumon systems across King and Snohomish counties. The panels are single pane tempered safety glass with deliberate ventilation gaps of two to three millimeters between them.

Those gaps are why the system survives our climate. Water drains, condensation escapes, and the framing does not rot. They are also why the space is not conditioned living area. You cannot heat a room efficiently when it is designed to breathe.

Adds square footage: no. Adds usable months: yes, and a lot of them.

A three-season sunroom

A glazed room, usually built on an existing deck or covered patio, with a roof and a real floor. Comfortable roughly nine to ten months of the year in this climate. Most of my clients keep using theirs through January with a small heater in the corner.

It is a room in every practical sense. It is still typically not conditioned space, because it is not insulated to code and not tied into the home’s heating system.

Adds square footage: usually no. Adds an appraisable amenity: yes, in the way a high end deck does.

A conditioned sunroom addition

This is a room addition that happens to have a lot of glass. Foundation, insulated walls and roof, code compliant glazing, ducted or ductless heat, permitted as an addition. It is warm in February without you thinking about it.

Adds square footage: yes. This is the only one of the three that reliably does.

Why Seattle homeowners keep picking the one that does not add square footage

Here is the part that surprises people. Once I explain the difference, most of them still choose the glazing.

The reasons are consistent. The glass system installs in a day on most balconies. It does not require a foundation. It usually does not require a permit if we are not altering the structure. It preserves the view completely, because there is no thermal break, no thick frame, no visual weight. And on a warm evening you slide the whole wall open and you are standing on a deck again.

A conditioned addition cannot do that last part. Once you insulate a room and tie it into the furnace, it is a room. You have traded the deck for interior space. Some people want exactly that. Plenty do not.

The other reason is money. Our balcony enclosures generally run $12,000 to $28,000 depending on linear footage, corner detailing, and whether we are touching the existing railing. Sunroom additions start around $45,000 and climb from there once foundation and mechanical work enter the picture.

If your goal is more usable outdoor space, the enclosure is the better buy almost every time. If your goal is a bigger house, it is not a substitute, and I will tell you that on the first visit.

What Seattle adds to the equation

A few local details change the math here, and they are the reason I do not trust generic national sunroom content on this topic.

Permits. In Seattle, an addition needs a construction addition or alteration permit through SDCI. Most balcony enclosures on an existing deck do not, because we are not changing the structure, but we confirm with the jurisdiction before we quote rather than after.

Lot coverage. This is the one that catches people. Per SDCI’s guidance on house additions and remodels, the combined footprint of all your structures, covered areas, and decks sitting 36 inches or more above grade cannot exceed a set percentage of your lot, and that percentage depends on your zoning. On a tight lot in Fremont or Greenwood, you can be maxed out before you start. A retractable glass enclosure on an existing deck does not add footprint. An addition does.

Energy code. Conditioned space has to meet the Washington State Energy Code. That means insulated assemblies and glazing performance targets. It is achievable and we build to it, but it is a meaningful driver of cost and it is why the wall assembly on a real addition looks nothing like a glass panel system.

Slope and soil. West Seattle, Magnolia, and half the Eastside sit on grades that make a new foundation expensive. I have quoted jobs where the geotechnical work alone changed the recommendation.

How I actually decide with clients

I ask three questions on the first visit.

What do you want to do in this space in February? If the answer involves working, sleeping, or hosting dinner without a coat, we are probably talking about a conditioned addition. If the answer is coffee, a book, a heater, and a view of the rain, glazing does that well and for a third of the price.

Do you need the number on the county record to change? Refinancing, selling within two years, or a specific appraisal target all push toward an addition. Nothing else really does.

Do you want to be able to open it? This one decides more projects than the other two. People underestimate how much they will miss the open deck.

There is no universal right answer, which is why I distrust any contractor who gives you one before seeing the house. Orientation matters too. A south facing lot on Mercer Island needs different glazing than a north facing one in Ballard under tree cover, and a covered patio in Redmond with a hot tub needs more ventilation than one without.

The hybrid nobody asks about

Worth mentioning because it comes up in maybe a fifth of our jobs. You can build a conditioned addition and glaze an adjacent deck or balcony. The addition gives you the square footage. The glazing gives you the open air space you just gave up.

If you are already planning deck work, it is much cheaper to design for this at the start than to retrofit it in three years. We frame and flash differently when we know glazing is coming.

Frequently asked questions

Does a Lumon balcony enclosure count as living space in Seattle?

No. The panels are single pane and the system ventilates by design, so it does not meet the definition of conditioned space. Appraisers in this market generally treat it as an amenity, similar to a high end deck or covered patio upgrade.

Can I convert a three-season sunroom into conditioned square footage later?

Sometimes, but it is rarely cheap. You are usually replacing the glazing, insulating the roof and walls, extending mechanical systems, and permitting the whole thing as an addition. If conditioned space is the eventual goal, build for it the first time.

Do I need a permit for a sunroom addition in Seattle?

Yes. Additions require a construction addition or alteration permit from SDCI, and smaller scopes may qualify for a subject to field inspection permit. We handle the submission. Balcony enclosures on existing decks usually do not require one, but we verify with your jurisdiction before quoting.

Which one adds more resale value?

It depends on the buyer and the house, and anyone who gives you a percentage is guessing. An addition adds measurable square footage, which is the more reliable path if resale is the reason you are building. Glazing tends to compete on lifestyle and photographs, and it does that very well on view properties.

How long does each take?

A residential balcony enclosure is typically one day on site once the Lumon panels are manufactured, and manufacturing runs four to six weeks. A three-season sunroom runs three to five working days on site. A conditioned addition is a different animal entirely, with permitting alone taking longer than the whole glazing project.

Where to go from here

If you are still unsure which one you are actually shopping for, that is the normal starting point, not a sign you have done anything wrong. The consultation is free and takes about 45 minutes. We measure the opening, look at the orientation, check for anything odd with the structure or your HOA rules, and tell you honestly which of the three builds fits what you described.

Star Construction WA 2220 164th Pl SE, Bothell, WA 98012 (206) 600-2225

We serve Seattle, Bellevue, Mercer Island, Kirkland, Redmond, Bothell, Renton, Issaquah, Sammamish, Lynnwood, Everett, and Mill Creek. Request a quote through our sunrooms and balcony glazing page or contact us directly.

Washington State licensed contractor #STARCCW791L5, bonded and insured. Authorized Lumon dealer for the Seattle metro.