Improving insulation

[Crakkers]

hi.

maybe 25 years ago the house I live in was extended. The kitchen was widened and a single pitch lean to tiled roof added above. When fitting some down lighters I think I noticed there is no more than about 50mm of loft insulation above the plasterboard. The kitchen is coldish and so I think it's wise to improve the thermal insulation, but can anyone recommend a diy and relatively straight forward method?

Thanks in advance.

 

[Crakkers]

No ideas?..

 

[CJRatch]

Overboard the ceiling with insulated plasterboard and skim.

 

[SmileyDan]

Unless you did it with an airtight box or a service void, you probably made the problem worse by installing downlighters, increasing air permeability. They are magnificent little chimneys.

Cheap, less effective, more error prone way: insulate internally as @CJRatch said (and ask yourself what to do about the downlighters).

Better way: tiles off, insulate between and over rafters, maintain continuity of air barrier with whatever is the air tightness layer in your current walls. If you don't have one, begin thinking how to have one and document what you do.

 

[Crakkers]

You are right about the chimney effect!

Not sure what you mean about "tiles off" its a plasterboard / artex ceiling.

How about I cut a big hole in the plaster board big enough to stand in to lay foil type insulation over the top of any existing. Then patch the opening and skim to new? Or as I have velux I could go through the side walls of the "tunnel" that goes from the ceiling to the pitch of the roof / velux.

Mad, but possible?

 

[tomfe]

Not sure what you mean about "tiles off" its a plasterboard / artex ceiling.

Take the tiles off the roof, it's a standard way to insulate a loft (normally single story) where there is no loft access and no mess inside.
Happens a lot on tenanted social bungalows.

 

[JP_]

Well, messy, and not sure I could DIY it myself, but I'd probably attempt to remove ceiling board and put 75mm insulation board between the rafters, maybe overboard with another 25mm, then plasterboard. Probably cheaper than putting insulated board on top, and more effective. But, more work ....

Suggested only because that is how my loft was insulated. Important to seal it all, as all that steam from cooking will condense on the rafters and rot them away.....

 

[jonshutt2]

Hi - just found this and wondering what you ended up doing with your ceiling? I'm interested as your kitchen sounds exactly very similar ours - the old kitchen wall was knocked out about 20 years ago to join the into an older out-building, with a lean to style pitch roof that goes up about 2m higher against the original house wall. Our roof is slated, and I assume solid wood planks under the slates (the rest of the house is), so I'm sure if we can come in from the outside...

I was wondering about just adding a layer of insulated board over the existing board, and also maybe also making a small loft space in the top part to bring the height down a bit - as I think all the warmth ends up there then seeps out. Or maybe it would be best to rip off all the old plasterboard and add it insulated board between the rafters as @jonbey suggests

 

[Ian H]

You would be better off with a full layer below the rafters if possible, rather than cut pieces between the rafters.

 

[Adam182]

You would be better off with a full layer below the rafters if possible, rather than cut pieces between the rafters.

I agree with Ian H,

However it wouldn't be optimal on its own because you would struggle to get a decent depth of insulation to make it worthwhile (unless you doubled up at the loss of several inches headspace). If it were me I would go for no less than 65mm between, foamed and taped and then a 38mm insulated PB to finish.

This method offers a great overall thickness of insulation and also removes the chance of cold bridging through the wood itself.

 

[jonshutt2]

Thanks @Ian H and @Adam182.

I'd rather loose room space then warmth! The ceiling is high enough not to worry about a few inches. If I'm going to effort of removing the existing plasterboard and therefore accessing the space between the rafters anyway, I'm happy enough putting insulation between and over - or just putting the thickest possible insulated board over the top - but I'm keen to avoid cold bridge/condensation issues. Thanks.

 

[Ian H]

There will probably be an online calculator or someone oh here that would be able to tell you the difference between having 70mm between the rafters and 50mm under then compared to having a full 120mm piece under them.

I’m no expert but i’d guess the 120mm under would perform much better.

 

[JP_]

why not do a bit of both? 70mm between rafters then another 100mm below? That'll be 50% more, and more will always be best in the longterm.

 

[jonshutt2]

Hi @jonbey - Yes, both seems to be an option, and what I'm currently thinking of doing. Thanks @Ian H for the advice about the online calculator - I've just found this: https://www.uvalue-calculator.co.uk/calculator/ which is really useful in terms of U-Values, and also suggesting techniques/relative thicknesses etc for various ceiling/wall types based