Mr Punter

Sorry @Russell griffiths I did not read the post too carefully and assumed you were adding an extra layer. Service void battens probably make the job a bit nicer as it makes the plasterboarding easier.

@DaveH @vivienz did this kind of thing. Not sure if it is what you are aiming for...

It is quite odd because there is not usually much wall above a window in a bungalow - just a course of blockwork then the roof overhang - unless it is a gable wall?

Doing some calcs the saving in heat loss would be 35W over the whole roof with a temperature difference of 10 degrees. Maybe you will save £15 a year on mains gas, £45 a year with full rate electricity, so between 3% and 8% or a payback of between 40 and 13 years. @Russell griffiths Are you costing in labour with your £600?

Hello Ebrahima and welcome. Did you get builders to do this for you? Maybe ask them what they were planning for the membrane. If you are not there you will need someone competent and trustworthy to oversee the work or you could waste your money and end up with a really shoddy job. As I am sure you are aware, building regulations in The Gambia are not enforced as strictly as the UK. Whereabouts are you building?

Maybe worth seeing if they would accept enhanced smoke detectors (mains linked one in each room plus corridors)

Maybe just some 40mm Celotex onto existing floor topped off with VCL and 18mm chipboard would be OK. Headroom probably not an issue if this is an understair cupboard.

You could just take the cill up and have a look.

It is very common. Very little effort goes into insulating window heads, cills and reveals.

https://www.rubberroofs.co.uk/installation

I just took delivery of a stone resin shower tray. I wonder if you could use a similar material and technique for a worktop?

Left hand looks like Siberian larch heartwood. Right hand looks like crap and not genuine. The Siberian larch I have had was all a similar (high) density. It looked fairly ginger in colour. It is slow growing and the growth rings are therefore fairly tight.

I have used EDPM on a large garage. It is cheap and fairly simple to DIY. I got it made as a single sheet but it was quite unwieldy. Joins, junctions, abutments, upstands and penetrations can be quite tricky, but I think this goes for many systems.

You can get the SE to prepare a tender package for the groundworks. If they are local they may have a few firms they will suggest. On the subject of muckaway but a bit off topic, a castle wall collapsed into the back garden of a building near me yesterday. They estimated 600 tonne of flint and chalk. It looks like it may be tricky to get at. https://www.theargus.co.uk/news/18030513.lewes-castle-wall-collapse-devastating-drone-footage-lays-bare-destruction/

Another decent week. Is this all being done on a price? Looks like it will be a high one!