Loft insulation - to top up or not? And other insulation musings

ChasingtheWelshdream

We have a large Edwardian house - solid walls, mostly solid floors downstairs. It isn't possible to insulate completely to modern standards, but we are looking to make improvements where we can, without compromising the building fabric and inadvertently introducing damp etc.

We have limited funds so need to make sure we target our money as efficiently as possible, so hoping you knowledgeable people can help?

First question: Our roof was replaced and we need to ensure the loft insulation complies with building regs to get building control sign-off. We currently have 270mm mineral wool, but this is approx 15 years old, dusty and dirty. We are going to partially board it out, but wondered if it is worth adding an additional 100mm or not? Will the existing insulation have lost effectiveness over the years or would this just be money better spent elsewhere?

Then we move onto the rest of the insulation areas. Which order would we be best to do the following?

Some rooms have coombed ceilings with no insulation and not accessible from above. We are going to overboard these with kingspan/cellotex.

Suspended timber floor - kingspan/celotex underneath.

External walls. In some rooms this is not possible, but where we are stripping out we can add some kingspan if not a full 100mm.

Solid floors - unfortunately a no go at present.


Regarding wall insulation - some rooms are going to be impossible to insulate all external walls without destroying 120 year old features, but can partially - eg underneath bay windows. Another room (kitchen) I can easily insulate one wall completely - the other isn't going to be possible without stripping everything out. Is it worth partially insulating these rooms does that make little difference overall? 

Many thanks - any input is welcome to help us form a plan of attack. 

FreeBear

If you have solid brick walls, I would recommend woodfibre ot cork boards with a pure lime plaster skim. Yes, it will cost a bit more, but the walls will thank you for it as you won't be trapping moisture behind the insulation.

grumbler

270 mm in the loft is good enough IMO and it doestn't get worth with time. Just make sure there are no gaps. 
Suspended floor - do you mean adding insulation between the joists, not under?  If you use hard insulation, don't leave any gaps unfilled.
And yes, insulating even one external wall in a room will make noticeable difference.

ChasingtheWelshdream

Thanks both.

Freebear - what about in a room which has previously been gypsum plastered with no (as yet) I’ll effects? 

Grumbler - What about when we can only partially insulate a wall? Eg, we have a bay window in a larger wall. Under the bay there is no insulation at all and we can sort easily. The rest of the wall would mean destroying all the original cornicing, which we don’t want to do from a conservation perspective. Would that be worth it?

Yes, for the floors we mean kingspan between the joists without restricting airflow.


Which order is it best to tackle? Ceilings- walls - floor?

This is long-term as we gradually put our house back together after other building works.

FreeBear

ChasingtheWelshdream said: what about in a room which has previously been gypsum plastered with no (as yet) I’ll effects?


Which order is it best to tackle? Ceilings- walls - floor?

Gypsum will still allow some moisture to pass through. But if remains damp for any length of time, it turns to a powdery mush.

Order of attack - I'd do the floor first, and then the walls & ceilings together.

ChasingtheWelshdream

Thank you. The floor is a priority in terms of comfort as there is a bit of a gale coming through so that is good to know. 

In terms of ceilings, and sorry to ask so many questions, is it worth over boarding the coombed areas (very large dormers and vaulted areas) before we do the walls? These seem the coldest rooms.

FreeBear

Are you planning on taking the plaster off the walls/ceilings ?

ChasingtheWelshdream

Not sure yet for the ceilings. Ideally not where they have been overboarded with plasterboard in the past, which seems to be the case with the coombed parts.

Walls - again ideally not but it depends on what other work needs doing at the same time. I am aware there is warm batten method which we would use if there is space.

ChasingtheWelshdream

The most pressing question is whether it is worth topping up the (old) 270mm existing loft insulation with another 100mm before we board it out (this weekend’s job) Or whether the diminishing returns are not worth it.

I am getting the impression that isn’t worth it?

FreeBear

If you already have 270mm, not really much point in adding more. But if you have a couple of rolls kicking around, it wouldn't hurt.

I already have ~250mm in my loft. As the ceilings come down, I'm stuffing another 100mm between the joists. Gets the stuff right up under the eaves and hopefully fills any voids where draughts might be blowing through.

ChasingtheWelshdream

Thank you. We would need to buy additional so if it not worth it then that is a saving right there. 🙂