The Complete Guide to Spray Foam Insulation in Houston

This is written for someone about to spend a meaningful amount of money on a building in Greater Houston, and it is written to be useful whether you end up hiring us or somebody else. Where the honest answer is “do something cheaper”, it says so.

Why the Gulf Coast changes the question

Most insulation advice on the internet is written for a heating climate. In a heating climate the enemy is conduction: heat leaving through the building fabric, which you fight with depth. Here the enemy is different.

Houston runs long, humid summers with attic temperatures far above the outdoor air, and in most of this metro the air handler and the ductwork sit directly in that heat. Meanwhile the building loses conditioned air through the top — the attic hatch, can lights, top plates, flue chases, every penetration a plumber or electrician ever made — and pulls hot, wet outside air in behind it to replace it.

That is an air problem. A ceiling with a foot of loose fill on it and an open plane underneath will keep taking humid air all summer, and the equipment will keep running to dry it. Which is why the first question about a Houston building is “where is the air moving, and where is the ductwork”. R-value comes second.

The three systems, and what each is for

Open-cell spray foam

Lower density, expands further, better at damping airborne sound, and vapor-permeable — which means an assembly can still dry, and a roof leak above it shows itself on the ceiling below. It is the usual specification at a conditioned attic roofline and in interior walls.

Closed-cell spray foam

Higher density, adds rigidity to what it is bonded to, higher R per inch, and at depth it acts as a vapor retarder. It sheds bulk water, which is why it is what belongs at a rim joist, in a crawl space, under an elevated floor, and against a steel panel.

Blown-in insulation

Loose material installed with a hose. It slows heat while air still moves through it. In a vented attic with sound decking, ducts that run inside the house, and a ceiling plane that has been properly sealed first, it is often the better buy — more area covered for the same money. The longer spray foam versus fiberglass comparison sets the two side by side.

Both foams are made the same way: two liquids that meet in the gun and react. If you want the chemistry, the A-side and B-side page covers it properly, including why ratio, temperature and pass thickness decide whether what you paid for actually performs.

The attic decision, which is most of the decision

There are two ways to insulate a Houston attic, and each suits a different building.

Sealing the roofline puts foam against the underside of the roof deck, closes the vents on purpose, and brings the attic inside the conditioned envelope. The attic then runs near indoor temperature, which takes the ductwork out of the hottest air on the property. This is the version that matters when your ducts and air handler are up there.

Insulating the attic floor leaves the attic vented and hot and puts the insulation on the ceiling below. It is cheaper, and it is right when the ducts are elsewhere, or when the roof is near the end of its life and the call on an unvented assembly is better made once the new roof is on.

One caution worth having early: some roof manufacturers have conditions about unvented assemblies. Ask your roofer before you commit, and get the answer in writing. The full detail is on the attic insulation and air sealing page.

The rest of the house

• Walls, where they are open. A renovation or a new build is the cheapest a wall will ever be to insulate properly. Once the drywall is back, the options narrow to dense-pack.
• The rim joist. A small area that leaks disproportionately, and on a raised or pier-and-beam foundation usually the best-value square footage in the building. See crawl space and rim joist work.
• The garage ceiling under living space, where a hot, unconditioned box sits directly beneath a bedroom.
• What is already there. Settled, wet or rodent-damaged material comes out first, because air sealing works on a clean deck. Removal is quoted separately so you can see what it costs on its own.

Buildings beyond houses

Steel behaves differently. The panel heats fast, radiates into the space, and then drops below dew point overnight so water forms on the inside and drips on whatever is underneath. Insulation stuffed between the purlins leaves the panel exposed to indoor air, so the condensing surface is still there. Closed-cell applied directly to the panel and over the purlins removes that surface, and the dripping stops.

That single fact drives most of our work in metal buildings, barndominiums, ranch and agricultural buildings and commercial and industrial envelopes. On the asset side — tanks, vessels and pipe — it is a different discipline again, driven by specification and corrosion where a building envelope is driven by comfort: oil and gas work.

What it costs, and why the price follows the visit

Spray foam is priced by board foot: square feet of surface multiplied by applied depth. Two attics with the same floor area can differ by half again on surface area alone, depending on pitch, dormers and framing. Add the access, the prep, the removal of whatever is already up there and how many times the rig has to be moved, and a phone quote is a guess.

What we can tell you on the phone is the band your job is likely to land in and whether an assessment is worth anyone’s time. The pricing and planning page lists what actually moves the number, and an assessment turns that into a figure for your building.

How to read a quote, including ours

A comparable quote has four things on it. With all four in front of you, you are comparing like with like:

1. The assembly. Which surfaces are being sprayed — roof deck, walls, rim joist, gable ends — and which are being left alone.
2. The system and the applied depth. Open-cell or closed-cell, and how many inches. This is the line that makes two prices comparable, and it is the line most often left off.
3. The exclusions. Removal, decking, electrical work, drywall repair — whatever is being left to somebody else.
4. The preparation. What has to be cleared, by whom, and what has to be complete before the crew arrives.

If a competing quote leaves the depth out, ask for it in writing. A contractor who puts a number of inches on paper is a contractor you can hold to it.

Where spray foam is the wrong answer

Being straight about this is more useful than another list of benefits:

• A vented attic that is working. Ducts inside the conditioned space, sound decking, a sealed ceiling plane — blown-in will do the job for less.
• An active roof leak. Fix it first. Spraying over water traps it in the assembly and hides it until the repair is much more expensive.
• A crawl space with a moisture source. The drainage and the ground cover come first. Sealing over a wet floor concentrates the problem.
• A finished wall. Foam needs an open cavity to expand into. A closed wall is a dense-pack job.
• A budget that only stretches one way. If the money covers either half the house in foam or the whole house sealed and insulated sensibly, the second is usually the better outcome.

Safety, cure and getting back in

The uncured components are reactive chemicals and need trained handling, protective equipment, work-area isolation and ventilation. Cured foam behaves differently from the liquids it came from. Re-entry timing is job-specific: the correct figure comes from the manufacturer of the product actually used and from the contractor who installed it, in writing, before the day. We publish what we do about ventilation and occupancy on the safety and re-entry page.

Doing this in Greater Houston specifically

The building science holds right across the metro. The building stock changes street by street. A Katy new build priced off a plan set, a First Colony attic full of settled material, an elevated house on the Galveston coast and a shop on acreage past Hempstead are four different jobs. That is why the site is organized by region: start at where we serve and work down to your city, or start from the building you own.

Whatever you do next — with us or with somebody else — get the assembly, the system, the depth and the exclusions in writing first.