The houses are now 50+ years old and many of the original roof slates are in very poor condition. There is very little insulation in the roof and the weatherboard areas are not terribly efficient either.
It is possible to replace the roof without touching the weatherboards, but if you want to improve the weatherboard insulation you will have to modify the roof at the same time.
The original roof has an insulation U-value of about 1.5 W/m2K. Adding 150mm of good-quality solid insulation board between the rafters will improve that to about 0.18 W/m2K. This should save about 20%-30% of your annual heating bill. Insulating the weatherboards will have less effect but is still worth considering.
We have developed some detailed specifications for these jobs:
- Roof Replacement Specification
- Roof Replacement Thermal Performance Calculation
- Roof Replacement Drawing
- Improving the Black Weatherboards – rationale, early proposals and thermal calculations
- Weatherboard Replacement Specification – includes description of design and the construction process
- Weatherboard Replacement Drawings – detailed design
- Weatherboard replacement bill of materials (PDF) – also BoM spreadsheet
- Weatherboard Replacement Appearance – document requesting approval by AGM
- Weatherboard Replacement Thermal Performance
- Extracts from the Accredited Construction Details: MCI-RE-04, MCI-RG-02, MEI-RE-04, MEI-RG-02
Following the pilot installation of roof and weatherboards at #2 in October 2020, we have a gallery showing all stages of the job:
Note that both jobs will require a Building Control application, though they should not require Planning Permission. If you use an accredited firm to do the roof, they may be able to self-certify the job.