Crawl space ceiling insulation

Otherwise known as insulating the floor joists. Every winter, people complain about cold floors – which is down to poor crawl space insulation between the joists. Historically, this always been installed in a particularly way, as defined in the building regulations. These specify R-19 fibreglass wool insulation with a (kraft) paper backing. If properly installed, the paper backing should be nearest the conditioned side of the floor (ie facing up towards the room). However, if the insulation has ever been replaced, it’s pretty likely that it has been installed upside down with the paper below the fibreglass wool in the mistaken belief that this stops the wool falling down.

Installed properly, fibreglass wool will help insulate between the crawl space and the warm inside of your home. However, it’s not perfect since the crawl space will always be cold unless you seal and insulate between the ground and the crawl space as well as between the joists.

One good way of doing this is to use rigid foam insulation panels rather than fibreglass – unlike a spray foam insulation, the foam panels can be removed for inspection but don’t sag or lose their thermal insulating ability when wet (which is a problem with fibreglass wool).

The government provides excellent reference material to help you tackle this tricky topic.

Read this account of the pitfalls if you insulate crawl space wrongly.

Insulation calculator

Using a standard three-bedroom home with a loft space of 44sq metres, here is the basic calculation:

Calculate how much loft insulation will save you

If you have no existing insulation – the cost to insulate to the recommended depth of 270mm will take two sets of rolls (one set 100mm thick, the second 170mm thick). Using our standard three-bedroom house, this will save you approx $220 / £175 per year. And the total cost of the rolls is approx $5/£3 per roll (note that this includes a carbon emissions saving factored in by the company selling the rolls and is for DIY use only).

If you already have a basic 100mm thickness of  existing insulation (common in properties that had some insulation fitted a few years’ ago) – then this is the insulation calculator for the cost to top-up  to the recommended depth of 270mm which will take one sets of roll (170mm thick). Using our standard three-bedroom house, this will save you approx $220 / £25 per year. And the total cost of the rolls is approx $5/£3 per roll (note that this includes a carbon emissions reduction target savings factored in by the company selling the rolls and is for DIY use only).

Dow insulation materials can be split into either spray foam insulation or rigid foam insulation.

Dow insulation – rigid foam

Dow’s distinctive blue STYROFOAM-A products FLOORMATE™-300-A, ROOFMATE™ SL-A and PERIMATE™DI-A  are used to insulate floors, roofs and basement walls of a structure. For the full range, visit Dow’s specialist website.

Dow insulation – spray foam

Dow’s spray products are marketed under the FROTH-PAK and STYROFOAM brand names. For the full range, visit Dow’s specialist spray foam site.

FROTH-PAK

Dow’s FROTH-PAK product is a foam insulation system made up of a two-component, quick-cure polyurethane foam that is used to fill cavities, cracks and expansion joints; it’s ideal for insulation and air sealing. It’s available in portable, self-contained kits or larger, refillable cylinders.

The Class-A rating (flame spread of 25 or less) of FROTH-PAK™ Foam Insulation allows its use in a wide range of industrial, commercial, institutional and residential applications in the United States and can be left exposed in non-fire-resistant rated roof/wall junctures as per National Fire Protection Association testing.