Insulation in cavity or inside the room?

Presumably sealed in at the eves/soffits?

No more so than if left uninsulated.

Or take the chance to do both - more overall, and less loss of internal space.

A bit depends on what kind of occupancy. Insulation inside is good for intermittent use spaces, since you can raise the internal temperature quickly since its decoupled from the bulk of the thermal mass of the masonry.

Full time occupancy can be better with more thermal mass inside the insulation since it takes longer to slew in temperature, thus keeping temperature swings down and reducing influence of very hot/cold days.

Find and read a copy of Approved Doc Part L and you will find info about perimeter insulation. New builds tend to have suspended block and beam construction which is grouted and overlaid with PIR insulation which minimises cold bridges at DPC level. Other methods are to have PIR under the slab which also has a band of perimeter insulation in order to reduce cold-bridging.

Cavity walls came about to prevent damp in solid walls buildings. 18" stone was fine, single skin brick on 50s was the problem.

Filling the cavity gives insulation, but it has inherent risk of damp, there are many claims of cavity wall insulation failures - it is fine if done properly, but would not be my choice.

Can you not build with Thermalite blocks, they are fully load bearing as long as you put suitable wall pate on top (standard practise) and lintols with correct bearing over any openings.

If BCO is involved (and legally he has to be) then he will insist that the construction complies with Part L anyway, which probably means thermal block inner leaf and either 50mm PIR + 50mm cavity or 100mm full-fill cavity with rockwool batts, then 100mm outer brick skin or

A close neighbour and also EOT and similar age property had the external insulation cladding (he is the South facing end of a 10 house terrace).

The house was sold (to the brother of the guy who lives at the other and of the terrace) and they noticed damp in the upper flank wall.

It turns out that the tiles didn't fully cover the end of the insulation and water was running / being blown underneath the outer roof tiles and behind the insulation and onto (the solid brick) wall. ;-(

Now it has nowhere else to go it ends up going though the wall and into the building. ;-(

They had some scaffolding erected and the bro from the other end did something (replaced the end tiles for wider ones to provide more overhang) in the hope to cure the problem that should never existed.

The problem is even if it was guaranteed work (maybe only to the initial owner?) many people wouldn't want such people back and so fund / provide the remedial work themselves. ;-(

Cheers, T i m

I'm thinking of doing the same to house a downstairs toilet/walk-in shower. What sort of size and budget do you have in mind.

Another Dave

The merits or demerits of having thermal mass (blockwork) inside the insulation have been well discussed before. Essentially it slows the warm up time and it slows the cool down time and may make a house a bit cooler in summer.

It's ideal for rooms in constant use as it helps keep the temperature even. Its bad for an occasional room that you want to warm up quickly.

I spent 2 months doing plans myself in inkscape, put them in a week ago.

Takes 2 months until i know if i can go ahead.

i have no budget worked out, but plan to save by doingh everything myself, except maybe fancy brickwork where the neighbours can see it.

The price of windows is frightening!

I will post more if i get planning permission

Thanks. I'm assuming it's permitted development as it's at the back of the (detached) house, several metres from the border and only a field behind the house. I'm not expecting too much windowing in a shower room!

I appreciate building control must be involved.

Another Dave

(sorry responding to the wrong post here, but can't see George's post in my feed)

It can be worth finding a maker of them to talk to, rather that a traditional vendor of windows. I found when I did my loft conversion[1] I got some quotes for several thousand initially. A bit of shopping about got that down to about £1k, then eventually I founds a window manufacturer in Romford that was happy to supply builders etc directly, and that got the price down to £570

Window 1 ? clear glass (MOE) 1800mm x 1200mm:

Window 2 ? obscure glass 1200mm x 1050mm:

Window 3 ? clear glass 550mm x 1050mm:

(note those prices are 18 years old now - so ignore the absolute numbers, and look at the differences!)