Plastic sheet under tiles

[JordanB]

I live in a mid-terrace house with a loft conversion done in 2006 (way before I bought the house). The loft room walls and ceiling are insulated with some sort of Kingspan stuff, but the eaves storage area (accessible via a cupboard/hatch) doesn’t seem to have any insulation at all other than Kingspan on the partition between the eaves storage and the loft room. The loft room is boiling hot in the summer and freezing cold in the winter, as is the bedroom beneath the eaves storage (you can feel cold air ‘falling’ on to your face when lying in the bed at night!)

Would putting Kingspan between the rafters of the eaves storage (and on the eaves storage boarded floor) help with the room temperature? There’s thin sheets of plastic under the roof tiles that aren’t taped together (I can slide my hand in the gap and feel the roof tiles underneath) but that’s it - can I just put Kingspan between the rafters on top of the plastic sheeting? Should I tape the sheeting together first?

 

[catlad]

Remove all the clutter and lay 300mm of loft insulation.

 

[JordanB]

Lay it on top of the boarded floor? The wool type?

What about between the rafters? Or should I try laying insulation on the boarded floor first and seeing how much difference it makes?

 

[robinbanks]

That plastic is a membrane used under tiles as a backup to catch water and fell it to the edge of the roof and into the gutter should a tile fail. It doesn't need taping together, has no appreciable insulative value and can be left alone. The gaps in it will help ventilate the area

If you choose to insulate your at the loft floor level and you have spare kingspan lying around I'd recommend using it to fill up between the ceiling joists with neat cuts that are a snug but not tight fit then go over the top of the whole lot with 200mm of wool. Don't kingspan all the way out to the edge, stop a few hundred mm short just use wool there. Reason being that kingspan is great and high performance but not much good if there is a channel for draught to get between it and the ceiling. Wool is less performant from an insulation perspective but great for deforming around things so there are no gaps for draughts, and it'll expand slightly so it's easy to place into the eaves area and achieve a good draught stop. You can alternatively spend hours messing about with expanding foam, but wool's definitely an easier fit. Don't pack it tight; it works better as insulation when fluffed up, not rammed in. Wear a breathing mask and a disposable suit. B&Q have quite good prices on it at the moment

If you want to use your eaves storage as storage after fitting wool, don't throw things on the wool, compressing it; fit loft legs before you wool and board out on top of them after

 

[robinbanks]

ps, I'm not sure with your post whether you're seeking to convert your eaves storage to have a warm roof; it currently has a cold roof, but if you're looking to change it to warm (and have it as a livable room) then you'd need to insulate between the rafters and underside them, then maybe plasterboard out the ceiling. You'd also need a strategy for dealing with air moisture generated by human activity depending on the insulation strategy chosen. If you've no plans to use the storage as a room, or only keep things in there that can cope with wildly changing temperature it's generally simpler to insulate the floor of the area and leave the wind to blow round above the insulation

 

[robinbanks]

The loft room is boiling hot in the summer and freezing cold in the winter

Did you mean to say the "eaves storage" rather than "loft room"? If the the loft room is lined with kingspan but still adopts the same temperature as the outside world then there's a problem with the insulation..

 

[JordanB]

Thanks for identifying what the plastic is/is used for and your advice about not taping it together. RE the purpose of the eaves storage – I only use it for storage (Christmas tree, suitcase, usual loft stuff!) but I’m convinced it’s at least part of the cause of the loft bedroom temperature differences and the ‘falling cold air’ in the bedroom below (I’d estimate the floor of the eaves is on top of about a third of the ceiling of the room below). I haven’t bought any Kingspan or wool insulation yet as wasn’t sure what I needed but as I’m trying to keep costs down, I think it’d be ok for me to use wool across the entire floor of the eaves storage (under loft legs) based on what you’ve said, and maybe ‘top up’ the accessible existing Kingspan lining the loft bedroom. The other areas that seem to let in cold are the two velux windows – they have thermal blinds but it seems the cold comes in around the edges of the frames so could they have been installed incorrectly? I’m looking to extend the loft dormer as a major future project (not DIY) which will involve stripping the loft bedroom back and re-insulating the entire thing to modern standards but I don’t think I can handle another winter sleeping in a freezing loft room, hence looking to try and do something semi-temporary now.

 

[JordanB]

One other thing that puzzles me is the fact the steel been in the ceiling (behind the ceiling plasterboard) appears to be uninsulated - I borrowed a heat camera and it clearly stands out! Should this have a layer of insulation over it?

 

[JordanB]

 

[robinbanks]

All vastly depends on the attention to detail when doing the work - I've seen loft conversions done by insulating between the rafters and then screwing plasterboards to the rafters; keeps insulation costs down (to not use it..) but a plasterboard->wood->world ceiling detail doesn't really have much in the way of a thermally insulative barrier between the world and the room. It's not clear from the infra red plot what the ceiling construction is - if the beam is visible in the room then it wont have any appreciable insulation. If it's boarded over, then there's probably nothing around it. The insulation barrier between the cold world and the warm envelope of the house needs to be continuous and of a minimum performance level - though that's not to say the steel should be insulated over; it could be that it's better to insulate under it, and leave it cold - insulating over it is less effective if its ends are jammed into two world-temperature walls, as it forms a significant thermal bridge across the insulation envelope

Could also do with a key on the image of what temp the other areas represent - we can see the beam is at 19.5, but if the white area is 23 it's quite a different story to the white area being 35. There are a lot of factors missing from that image to give any more than a basic interpretation; need to know a lot more about the environment on the day it was taken

"I’d estimate the floor of the eaves is on top of about a third of the ceiling of the room below"

You mgiht well see something expected if you point your thermal camera at that ceiling - this two thirds warm, that one third cold. Coupled with a heat source (radiator) under the warm area and it'll set up a cycle of air movement where the air is heated here, rises and spreads to the cool bit on the other side of the room, falls because it's coolar, then scoots along the floor to where it's warmed again - a convection cycle (and why we put radiators under windows, so the rising heat and falling cool meet and mix near the window rather than cycling round the room creating a draught

If all youre doing is throwing a christmas tree in there, you could get away without log legs and boarding, just wool the whole area out, and throw the tree on top of some plastic sheet on the wool. I was more thinking you might be wanting to put your old LP collection up there..

Terms of compalint that the loft room is cold despite allegedly having insulation, you need then to look at where it gets its heat from. If the room is insulated at floor level (because the roof used to be cold) as well as ceiling then it's blocked off from acquiring a good amount of the heat it would normally get from downstairs. If the room has heating or access to warm air then a quick nose around with the thermal camera will tell you where the cold spots are that are sucking the warmth out of the room