Mould
Light surface mould on the rim or sill is common. We clean small areas and treat them before spraying, and larger growth goes to our mould removal process.
The fastest-payback job in most homes
Rim Joist Spray Foam Insulation in Guelph
Super Sprayers seals rim joists in homes all over Guelph, Kitchener, Cambridge and the smaller towns around them, and it is the job we recommend first more often than any other. Since 2018 we have completed more than 800 insulation projects, and a large share started with a homeowner complaining about cold floors, a draft along the baseboards or mice showing up every October. In most of those houses the rim joist was the culprit, stuffed with a loose piece of fiberglass that never stopped any air at all.
The rim joist is the band of lumber that sits on top of your foundation wall and holds the ends of the floor joists. It is thin, it is exposed to outside air on one side, and it is riddled with gaps where the sill plate meets uneven concrete. Air pours through those gaps, and in winter the cold air sinks straight across the basement floor.
Closed cell spray foam fills every one of those gaps and insulates the wood in the same pass. On a typical detached house the job takes a few hours to a day, the difference is noticeable the first cold night, and the cost is modest compared with almost any other upgrade. Our crews are CUFCA certified, WSIB covered and follow the CAN/ULC-S705 installation standard.
- In business since 2018
- 800+ jobs completed
- WSIB covered, licensed and insured
- 2-year labour warranty
- 5-star Google rating
Why Rim Joists Leak So Much Air
Foundations are rarely perfectly flat, so the sill plate sits on a wavy surface with gaps underneath it. The joint between the sill plate and the rim joist, and every joint between joist ends, adds more cracks. Pipes, dryer vents and wires punched through the rim add even more.
A batt pushed into that corner slows heat a little but lets air straight through. Worse, warm basement air reaches the cold wood behind the batt and condenses, which is why we often find the wood stained or mouldy when we pull the batts out.
How We Spray Rim Joists
- 1
Pull the old batts
Loose fiberglass comes out and gets bagged for disposal.
- 2
Clean and inspect
We vacuum dust and droppings and check the sill plate for rot, mould or insect damage.
- 3
Seal penetrations
Gaps around pipes, vents and wires are sealed so nothing is left behind the foam.
- 4
Spray closed cell
2 to 3 inches of foam goes on the rim, sill plate and joist ends in controlled lifts.
- 5
Clean up
Masking comes down, the area is swept and you can use the basement after the re-occupancy time.
Spray Foam vs Cut-and-Fit Rigid Foam
Rigid foam board cut to fit each bay and sealed with canned foam is the common DIY method. It works if done carefully. Here's an honest comparison.
| Factor | Spray foam | Cut-and-fit rigid foam |
|---|---|---|
| Air seal | Excellent and continuous | Good, if every edge is sealed |
| Time for a typical house | A few hours to a day | One or two weekends, DIY |
| Cost | Higher | Lower in materials |
| Irregular bays and pipes | Fills around everything | Slow and fiddly to cut |
| DIY feasibility | No | Yes |
If you enjoy DIY and have a simple basement, rigid board is a fair choice. Our DIY kit vs professional guide covers the trade-offs, including spray foam kits.
Headers Between Floors
Two-storey homes have a second rim joist, sometimes called a header, where the upper floor sits on the main floor walls. It leaks just like the basement one, but it's hidden inside the wall and ceiling, so we reach it during renovations or from below where a garage ceiling or cantilever is open. The between-floor insulation page explains how.
What We Find Behind Old Rim Joist Insulation
Rot
Soft or crumbling wood gets shown to you before we spray. A carpenter needs to repair structural damage first.
Mouse nests
Batts in the rim are a favourite nesting spot. We remove the nests and droppings with a HEPA vacuum and seal the entry points.
Rim Joist Cost and Timing
Rim joist jobs are priced by the linear feet of rim and the thickness of foam. Most detached homes in our area fall between about $1,000 and $2,000, and most jobs are finished in a single visit. Tight access behind ducts and finished ceilings, heavy cleanup or rot repair raise the price.
Rim Joist Questions
Should the old fibreglass come out?
Yes. It has to come out so the foam can bond to the wood and seal the gaps, and it's often dirty or mouldy anyway.
How long does rim joist spray foam take?
A few hours for a small bungalow, up to a day for a large house with lots of pipes and ducts to work around.
Does foaming the rim joists keep mice out?
It seals many of the gaps mice use, which helps a lot. Our spray foam and pests guide explains what else to do.
Related Services and Resources
- Basement Spray Foam Warmer floors and no more damp, musty corners.
- Air Sealing Find and seal the leaks that make a house drafty.
- Between-Floor Insulation Fix the cold bonus room over the garage.
- Spray Foam and Pests What foam does, and doesn't do, against mice.
- DIY Kit vs Professional When a spray foam kit makes sense, and when it doesn't.
Free estimate
Book Your Rim Joist Job
Tell us the rough size of your basement and whether any part of it is finished. We can often book rim joist jobs within a week or two.
- Call or text226-780-8752
- Emailinfo@supersprayers.ca
- Mon to Sat: 7:00am to 9:00pmSun: 9:00am to 6:00pm