The house has three separate roof areas, and luckily for this blog, three roof types. The main roof is has around 50mm mineral insulation between joists. The front of the house has a bay with its own small roof which has been modelled with no additional insulation installed.  The rear extension has a flat roof that was replaced in the mid 90s.

I’ve used our masterplan software to model the changes – I’ve set the base model to have a top efficiency boiler rather than the antiquated heating systems that are currently in place as I will definitely be changing this.

Bay Roof
The bay roof has been modelled with around a U value of 2.  There also is not much space to add additional insulation.  What are the options?  The void can be filled with insulation – some mineral wool or potentially something with a greater insulation value for smaller depth such as XPS or even more such as PIR or phenolic foam board.  This could be added from the outside but would require the tiles to be removed, or internally but would require the ceiling to be removed.  Another option is to insulate the inside face of the ceiling of the bay window.

Since I will be taking some polystyrene ceiling tiles off the ceiling of the room, and also I want to look at the timbers of the floor above I will be taking the internal ceiling of the bay down. I’ll then insulate with foam board and then apply new plasterboard.
Estimated cost: £50 (DIY measure)
Saving: £3.30
Payback: 14.79 years

Flat Roof
The rear roof is a flat roof built in the mid 1990s and probably has a U value of around 0.35.  A new Building Regulations roof would need to have a U value of 0.18 or better.

If the roof was in good condition it could be insulated on the inside to keen the costs down.  In this case the roof requires some work to weatherproof it.  Strictly speaking this means it will need to be brought up to Building Regulations anyway. Scaffolding will probably be required to carry out weatherproofing works so I will be looking into quotes to bring it up to current Building Regulations as well as getting a solar thermal system installed on it at the same time.

Estimated cost: £1,000 (Professionally done)
Saving: £3.56
Payback: 281 years

Main Loft
The main loft is a standard pitched roof with around 50mm of insulation installed between the joists. This insulation is in a pretty badly installed.  Cheapest and easiest solution is to top up the insulation between and over the joists to 300mm.
Estimated cost: £250 (DIY measure)
Saving: £45.48
Payback: 5.5 years

Another option being considered to have a central area that has 100mm mineral wool between the joists and XPS board insulation and chipboard above the joists so that a solid platform remains for storage.  this will cost a little more but should result in similar savings.

Whist I’ve got the loft ladder out I’ll be carrying out some work on the loft hatch:

Loft Hatch Insulation
Estimated cost: £10 (DIY measure)
Saving: £2.32
Payback: 4.3 years

Loft Hatch Draughtproofing
Estimated cost: £7.50 (DIY measure)
Saving: £2.09
Payback: 3.6 years