Our customers often asked, "Should I combine different types of insulation, or is that just unnecessary work?" In response we offer our personal opinion, which is given without prejudice. We always recommend that our customers check with their architect, designer, building control officer, and/or read the product literature and datasheets before making any decision to install or purchase.

PUR/PIR and Multi-foil Insulation? Or, Thinsulex and Celotex, if you prefer ...

The benefits of combining PIR Insulation boards with Actis Super 10 or Thinsulex Silver ...

Commonly, we are requested to quote on insulation for a roof that has to achieve a U-value of 0.2. And our most common comparisons are ...

Celotex Extra-R XR4000 - 150mm board costing £16.15 per m2.

versus ...

Celotex Tuff-R GA4070 - 75mm Board @ £8.10 per m2 and Gen-X 33mm @ 5-8 Rolls x 12m2 Rolls @ £7.39 per m2 - a combined cost of £15.49 per m2 and with no need for foil-backed plasterboard (a £2.00 +/- saving) if GeneX installed below the rafters

or ...

Celotex Tuff-R GA4070 - 70mm Board @ £7.62 per m2 and Thinsulex Silver @ 5-8 Rolls x 12m2 Rolls @ £7.56 per m2 a combined cost of £15.018 per m2

or ...

Celotex Tuff-R GA4050 - 50mm Board @ £5.49 per m2 and Actis Super 10, 3-6 Rolls x 20m2 @ £9.02 per m2 - a combined cost of £14.51 per m2

(These prices were correct at the time of writing)

It should be noted that Celotex, Gen-X and TLX Silver all have BBA Certification, so there should be no problems with Building Control. Actis Super 10 has a BM Trada Certificate, and will not necessarily be acceptable to Building Control.

 

It can be seen that the price difference is not dramatic, so what are the other 'Pros' and 'Cons'?

150mm PUR/PIR Boards and 150mm Rafters

Generally, an airspace will be required between the the breather membrane/roofing felt and the insulation. The result, with 150mm PUR/PIR board is that the insulation will protrude below the rafters, resulting in the requirement for additional batten.

70mm PUR/PIR Boards plus Multi-Foil and 150mm Rafters

By placing the 70mm boards midway down the rafter leaves a minimum of a 40mm airspace top and bottom. Multi-foil can then be stapled to the bottom of the rafters.

Benefits of adding Multi-foil to the mix ...

As we have seen multi-foil insulation can reduce space requirements over traditional insulation products, at no extra cost.

PUR/PIR boards may not fit entirely snugly between the rafters or joists. By adding multi foils the envelope of the property can be sealed to inhibit unnecessary air movement.

Unlike PUR/PIR boards, multi-foils will reflect Infra-red energy into the building in winter, and reflected back into the atmosphere in summer.

By combining traditional boards with multi-foil, the benefits of both types of insulation amalgamate to provide better insulating qualities.

Glasswool and Multi-foil Insulation? Or, Earthwool® RaferRoll 32 plus Gen-X, if you prefer ..

The most recent multi-foil insulation to be added to our stock is BBA Certified Gen-X 33mm.

Combining Gen-X with Earthwool® Rafter Roll 100mm will achieve the required U-value of 0.20, and obviates the need for foil-backed plasterboard when GenX is installed below the rafters.

Earthwool® Rafter Roll 32 - 100mm semi rigid Roll = @ £9.98 per m2 and

Gen-X @ 5-8 Rolls x 15m2 Rolls @ £7.39 per m2

a combined cost of £15.37 per m2 ... plus a £2.00 +/- saving on the Plasterboard

 

Page last updated Monday, April 16, 2012