The part of a quonset that fails first is the part nobody looks at. Quonset spray foam insulation in Brooks is worth planning from the ground up rather than the top down, because on an arch building the base of the curve - where the steel lands on a footing, a knee wall or bare gravel - is doing the hardest work and getting the least attention.
The bottom of the arch is where the water ends up
Everything that condenses on the shell runs down the curve, and everything that runs down the curve arrives at the bottom. So does splash from outside, snow drifted against the wall, and moisture wicking up out of the ground. On irrigated ground the water table and the surrounding soil moisture make that last one more than a theoretical concern. The lower edge of a quonset is a wet zone in a way the top of the arch simply is not.
How the foam has to be terminated
Where the insulation stops matters. Ending it a foot above the floor leaves a cold band of steel below it, and that band becomes the new condensation surface with the water running behind the foam above it. Carrying it down to the base and detailing the termination so that water cannot get behind the material is the part that makes the difference. It is not difficult, but it is skipped often enough to be worth asking about specifically.
A knee wall changes the job
Many arches here sit on a low concrete or block knee wall rather than directly on a footing. That wall is a different material with a different temperature, and the junction between it and the steel is a joint that moves seasonally. Foam is useful there precisely because it is applied as a liquid and bonds across two dissimilar surfaces, which nothing cut to size will do reliably.
Ground moisture is not solved by insulation
If a building sits on gravel or dirt, the floor is a continuous moisture source that keeps releasing into the air regardless of what the shell is doing. Insulating the arch stops the water condensing overhead and landing on what is stored below. It does not remove the water from the building. Where product is being stored long term, a ground vapour barrier or deliberate ventilation does the other half, and we would rather name that than let the arch take credit for it.
Why the shape rules out everything else
There are no stud bays and no flat planes on a quonset. Batt has nothing to sit in and rigid board cannot lie against a curve without leaving voids, and voids against cold steel are where the water collects. Foam bonds to the shell and follows it. It needs clean, dry steel and any active rust dealt with rather than sealed under.
Quonset Spray Foam Insulation Brooks: Common Questions
Where should the insulation stop at the bottom? As low as the detail allows. Stopping partway up leaves a cold band of steel that becomes the new condensation line. On the Brooks buildings we are called to, that band usually sits just above the concrete.
Our arch sits on a low concrete wall - does that matter? It does. That junction joins two different materials and moves seasonally, and it is one of the places foam is genuinely better than anything cut to fit.
Will insulating fix a damp gravel floor? No. It stops the water condensing overhead. Ground moisture needs a vapour barrier or ventilation, and we will say so.
Estimate the thickness with the R-value calculator, then get a free Brooks quote. More on Quonset Spray Foam Insulation Alberta province-wide.