Cold bedrooms, condensation on curved ceilings.

[plastic_peanut]

I insulated my loft a couple of months back using 200mm encapsulated space blanket over the top of the existing insulation.

Just after Christmas I noticed a lot of condensation had appeared and decided to remove the encapsulation from the new insulation and check the eaves above the curved ceilings. Some were packed with insulation, I found old expanding foam and birds and wasp nests.

I was able to clear the eaves using a long piece of wood but I intend to get back up there and vacuum the debris from the eaves and insulate. I am conscious of not restricting air flow so was thinking of a thinner insulation slab on top of the slopes section similar to that in the picture.

I may then add lap vents. Due to the limited clearance is there a suggestion of which insulation to use please? I was thinking slabs just for ease and being compacted should help prevent blocking air movement

 

[SimonH2]

What sarking sheet material do you have ? If it's the old tarred felt then that's impermeable and you need an air space and ventilation to allow airflow - otherwise you'll get condensation. If it's a modern breathable membrane then AIUI you can rely on that to let the moisture out.
Here's some photos of what I did with my rooms.
Battens on the rafters, first layer of board between teh rafters and all the joints foamed in. Cut off the excess foam, then another layer of insulation underneath. Finally the new plasterboard (and plastic sheet), fixed with thin fixings* to try and avoid creating cold spots with lengths of steel bar conducting heat through the insulation - that's the theory anyway :

And one cold morning, I got a snap of the frost on the roof. You can see that the bathroom (to the right) has a lot less front on it, and the neighbours (to the left) had b***er all frost left on. At this point, the main (flat) ceiling still needed some insulation adding, so the sloping bit was the best insulated of all :


BTW - I put a sheet of plastic between the plasterboard and the insulation to keep room moisture in the room so it can't permeate into the insulation and condense there.

* Don't look too closely, those aren't actually the right fixings - they sent the wrong ones, but I didn't have time before the plasterer was booked to get the right ones

 

[Fozi]

Can the curved ceiling just be overboard with insulation board. I will need to instruct a builder but not sure what to do as the curved ceiling attracts lot of condensation. Not sure how the loft space is but I am assuming that there is no insualtion in this area in the loft. Can insulation be put in this area through the loft. If so what type will I use. Do not want to use foam insualtion as it is difficult to remove if need be.

 

[SimonH2]

Read the earlier posts - all the options have been described !
With "some effort" you should be able to slide slabs of insulation down from inside the loft. But because the ceiling joists will be nailed to the side of the rafters, you'll need to cut each slab into 2 - so you can pass one of them down and slide it across behind the end of the joist before sliding the other in alongside it.
Or you can lift off the tiles and work from above.
Or pull down the ceiling and re-do it.
Or you can just over-board the existing ceiling.

IMO, the most effective method is to pull the ceiling down and re-instate it after insulating properly. It's messy, and it makes more of the sloping bit in the room, but it gives you as much insulation as you want with minimal cold bridging. It's also the most disruptive and best done when doing other major works - in our case, both bedrooms needed some walls re-plastering from the bricks up and I was doing other work (adding sockets etc) as well, so the disruption didn't really matter.

It is important that the insulation fits well. If using batts of (say) rockwool, then they need to be a tight fit. If using rigid foam, then they either need to be a tight fit (fiddly to do) or you need to foam all the gaps. If you have gaps round the insulation, then air will circulate and reduce the effectiveness of the insulation.

 

[plastic_peanut]

Simon thanks for taking the time to provide all the information. I don’t have any condensation issues on the bedroom ceilings I am looking at it really to prevent heat loss. The flat sections are fully insulated but the slopes aren’t.

I went in the loft today and using a good length of PVC pipe attached to the hoover I was able to remove anything in the eaves space. This was old foam insulation, nest etc.

This was beneficial as it confirmed we do have a leak near the chimney so gave me confidence in employing someone to rebuild and weather proof it. I was able to remove damp material as well so pleased i did this.

I intend to slide insulation slab down the eaves to maintain an air gap. I intend to use 100mm omnidirectional slab to hopefully help with the handling.

 

[Fozi]

Can anyone recommend a tradesman who can do this job for me.

 

[Fozi]

If I decide to overboard, is there any chance condensation will just occur underneath the insualtion board.

 

[SimonH2]

I don’t have any condensation issues on the bedroom ceilings I am looking at it really to prevent heat loss.

You are lucky. Cold surfaces like these are where moisture condenses - and when it gets bad enough then mould will grow. Even without mould, those cold surfaces will be damp deep into the materials.

I intend to slide insulation slab down the eaves to maintain an air gap. I intend to use 100mm omnidirectional slab to hopefully help with the handling.

How deep are the rafters ? Likely 3"
If so, then you'll only get 50mm in the gap while leaving an inch gap.

 

[plastic_peanut]

Thanks Simon, yup 3”. I can see B&Q have some 75mm insulation slab on offer.

Far cheaper than the omnifitnstuff. I will give that ago as it seems less intrusive but I admire your approach to resolving the issue. Thanks for your advice

 

[Keithmac]

We've got exactly the same problem!, this is great thread with some excellent ideas.

Thinking of pulling a stip of plasterboard off the sealing where the curve is and maybe packing the rafters to get some decent thinkness of insulation in.

Really poor design.

 

[SimonH2]

Don't forget that these houses were built in different times - our current house dates from the 1940s.
Back then, the rooms weren't heated, so to a large extent, heat loss wasn't important. Windows didn't seal (and had single glazing), and the effect of having a coal fire going in the living room was to draw air through all the rooms.
That's why condensation on walls/ceilings wasn't a big problem. Windows were a different matter, mopping them every morning and scraping off the ice in cold weather was just routine.

In context, they were a massive improvement from some of the overcrowded slums the post war social housing program was created to replace. Houses that didn't rain in, with rooms that were reasonably sized. Gardens so children could experience "an outside". For the time, they really were good houses. In fact, construction wise, they tend to put modern "build 'em as cheap as we can get away with" commercially built homes to shame.

What's wrong now is that we've taken the same design, fitted sealed windows, blocked up the vents, and expect the same moisture created inside to not cause problems
Rant mode : and now we have building regs that in the name of energy efficiency mandate airtight houses. And then to mitigate the problems that causes, mandate vents etc to re-introduce the air leaks

 

[John D v2.0]

In context, they were a massive improvement from some of the overcrowded slums the post war social housing program was created to replace. Houses that didn't rain in, with rooms that were reasonably sized

That's a really interesting comment, in fact my grandad said the house he was born in when it rains the water ran in the back and out the front, flag stone floor.
He described the 1920s house we bought as "a modern one built with the flushing toilet indoors and the electric supply"! Although the build quality was average if that,i don't think house building quality has necessarily gone downhill much since then!
I wonder what we will be saying in 50 years time about the new houses.

 

[cwhaley]

Just to add to the above two comments, the YouTube video below links to a documentary made in 1969 describing the condition of houses the people of St. Ann's in Nottingham were living in. It's a localised documentary obviously but a fascinating insight into the third world conditions people were living in during the year we landed on the moon. It will put into context the comments said above.

The pub which features at the start (Hero of Waterloo) was owned by my great grandad's brother and was demolished in 1970 when they cleared the entire area.

 

[Keithmac]

Just been looking at Insulated Plasterboard, the Kingspan is ££££!.

Is there any alternative that is any good?.

 

[cwhaley]

Celotex or look for 2nd hand off-cuts of either on selling sites -- there's usually loads.