GBE Spray Foam Thermal Insulation Q+A

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Spray foam is a temporary solution to achieving airtightness.
Air leakiness enables heat loss or coolth gain and combined with moisture vapour, risks of condensation, mould, rot, structural failure and frost damage.
If the surfaces it is sprayed onto are not clean, dry, dust-free, primed, the risk of the shrinking foam will not adhere and pull away, no longer airtight.

Spray foam is usually hydrocarbon (a finite resource) petrochemical plastic from fossil carbon oil and with potentially polluting chemical process waste
There was a bio-based foam (rapidly renewable, plant based, carbon negative due to carbon sequestration) on the market, but when challenged by a specifier, found keeping supply chain audit trails to sustainable sources challenging and they switched to back to petrochemical.
A too clever-clog specifier (might even be a violet) that caused a switch from carbon-negative to carbon-positive resource.

Closed-cell foamed-plastic is usually air-tight and moisture vapour tight; so it is risky in conjunction with timber construction
The insulation create barrier to moisture permeability and the only way out is through the timbers
Some older roofs have been destroyed by enveloping the timbers so unable to breath and keep dry.
There is a video showing lumps of the insulation being pulled out of the installation and squeezing water from the foam.
That video did not interrogate the cause, just the symptoms, so we do not know if it was caused by:
- leaking roof,
- surface condensation from the underside of the roof tiles
- interstitial condensation in the foam.
There is one manufacturer that produces an open cell moisture permeable sprayed foam insulation

One badly behaved manufacturer/installer has instructed a second team of installers to spray roofs where bats were known to roost, discovered by their first team who declined to do the work, and trapped or entombed hundreds of bats to die.
£5000/bat fines should be enough to stop this behaviour

There are numerous examples of where the occupants have suffered ill health due to off gassing from foaming plastic insulation, so bad that they cannot re-enter their buildings.
Effectively destroying their investment.
Nuff said?

Rigid board foam insulation probably does not snug-fit against timber frame members.
Cutting to profile, using a blade could be good, but not easy
Cutting with a hot-wire will probably produce toxic smoke or emissions.
Cutting with a saw will produce millions of micro-plastics that will not normally be collected, so will be wind blown and work its way into drains, sewers, to the oceans.
‘GapOtape’ solves the leakiness issue by wrapping the edges of the boards with a foam strip adhered with self adhesive aluminium foil.
But using airtight insulation between timber framing seems instinctively wrong.

Limited access can mean insulation of a suspended ground floor needs to be insulated from above after removing the floor boards.
Using a purpose made support system stapled to the floor joists then batt insulation installed from above.
See Insumate product range Accessories in right column
Then regularised and sanded boards can be relaid

There is a system of insulating using a robot on wheels to spray foaming insulation into the joint zone from below.
This still needs to be moisture permeable and wind resistant and conductivity thermal insulation
It does not need to have specific heat capacity since the sun does not reach here.