insulating loft of thatched cottage

[shobo]

Anyone ever done it ?
I have a grade II listed thatch with lath and plaster ceilings in quite good condition.
The thatch itself is very tidy inside, and the floor of the loft (ie the top of the lath and plaster ceiling) is clean and debris-free.
Cold water storage tank and pipework is in the loft.
The roof space is perfectly sealed - there are no drafts whatsoever.
Currently I have heating by individual electric heaters - so the heating system doesn't have much oomph - but I have a planning application pending for central heating (though actually I haven't decided on it yet).
I have been thinking of insulating the loft floor in the conventional way using rockwool then possibly overboarding - but probably won't, for the reasons below (especially 2 and 4):

1. it may convert the loft from a warm loft to a cold loft, this may not normally be a bad thing, but are there any disadvantages of this to the thatch.
2. if in future it is necessary to repair the lath and plaster ceiling,the insulation and boarding would be an impediment and would probably have to be removed.
3. when the thatch is re-done (I imagine complete removal of the old thatch) would the insulation and boarding be an impediment to that.
4. the weight of the rockwool, though low, combined with a little bit of pressure from pushing it down, could damage the lath and plaster.
5. thatch itself is a good insulator, so perhaps the advantages of insulating the loft are minimal.

Any comments, anyone please ?

 

[CliffordPope]

Lots about the insulating properties of thatch roofs here:

https://historicengland.org.uk/images-books/publications/eehb-insulating-thatched-roofs/

 

[88v8]

A bit of insulation will do no harm. Even though thatch is a good insualotor, you are still heating an empty space.

Our thatched roof lofts are both insulated. I put rockwool up there, just up to the thickness of the joists, not over the top.
Then I partially overboarded them.
One loft is new, well, it dates back to the 60s when the house was extended.
So its joists are level and the ceilings are plasterboard.

That one I fully overboarded for storage. But, not under the cold water tank. Important !!!!
And making the loft cold means that the water pipes have to be lagged with fanatical care, no little gaps.

In the old loft, I just overboarded an area I can reach from the hatch when standing on a ladder. That's because the joists are not strong enough to bear my weight without deflecting. They're about 2x2", elm, quite strong, but never meant to be walked on. Deflection would crack the excellent lath & plaster ceiling.
And indeed they had never been walked on until I made an access hatch, because the space was sealed when the ceiling was put up about 200 years ago.
So not only did I not overboard the whole loft, but I didn't screw the boards down because that would also stress the joists. As you say, they are not level. I actually used plywood, and just laid it loose. All I keep up there is very light stuff - Xmas decorations, light bulbs, bit of spare china.
Another reason I did not lay the insulation thicker than the joists is that if I did, the boards would compress it, which stresses the ceiling.

Couple of points: if your thatch has ever been totally renewed, it may have felt or something under the thatch. So the loft will be fairly dust-free. That is the case in our new loft.

But in the old one, the underside of the thatch is just loose straw, probably 400 years old, It sheds dust and bits & pieces in a constant rain. Not really a place for storage.

There should be no reason to work on your lath ceiling, Unless you have a disaster. So that's not a reason for omitting insulation. Assuming no one falls through the ceiling and the water pipes don't burst, that ceiling should be regarded as a permanent feature.

Btw, unless it's really rotted, thatch is not removed when rethatching. Just the top layer, then more is put on. So the underside should never be disturbed.
The only part that gets completely removed is the ridge - if you have a straw roof, that will need doing every 8/10 years, with a complete rethatch every 30 years or so.

We have storage heaters on Economy Seven & woodburners. I decided not to install central heating due to the disruption. After all, previous owners have managed 40+ years with it as it is, why shouldn't we.........

Yes, insulate away!!

Ivor

 

[MatthewC]

A bit of insulation will do no harm. Even though thatch is a good insualotor, you are still heating an empty space.

Our thatched roof lofts are both insulated. I put rockwool up there, just up to the thickness of the joists, not over the top...

Ivor - rockwool? Are you meaning the old roof or the new(-ish) one? I would have expected you to use a proper sheepswool product so that it breathes.

The roof space is perfectly sealed - there are no drafts whatsoever.

If you go for a cold loft then you need some draughts to ventilate the loft space. Any moisture that gets in needs to get out again!

I used Thermafleece in my loft, on top of lath and plaster ceilings. Having laid rockwool in the past I found it quite horrible to work with, as well as being quite useless if it ever gets damp, because it then compacts and never really dries out. Thermafleece has a small amount of plastic in it in order to maintain the body - it doesn't compact even if wet.

 

[george2019]

A bit of insulation will do no harm. Even though thatch is a good insualotor, you are still heating an empty space.

Our thatched roof lofts are both insulated. I put rockwool up there, just up to the thickness of the joists, not over the top...

Ivor - rockwool? Are you meaning the old roof or the new(-ish) one? I would have expected you to use a proper sheepswool product so that it breathes.

Mineral wool is vapour permeable. The material itself is water resistant.

 

[shobo]

Thankyou all,
especially Ivor - your experience is so similar to mine.
I also have considered central heating, but I have now gone off the idea somewhat. There would be a lot of disturbance to the fabric of the building, and now we are in our second winter in the cottage, I am getting used to the electric heating, and feel that its a warm cottage - its not affected much by cold snaps - tends to stay purring at the same temperature like a contented cat.
It hadn't occurred to me that stepping on the loft beams could disturb the ceiling - actually I wonder if this has happened already, there is a bit of a crack around the loft hatch which I am not sure was there previously. So that's reason no. 8 for not insulating the loft.
btw my heating is not Economy 7, it is powered once at night then again for two hours in the afternoon. I am quite pleasantly pleased with how not-as-expensive-as-I-thought it would be to run. It would be nice if there were a central control point to switch on the heaters remotely.

 

[88v8]

It hadn't occurred to me that stepping on the loft beams could disturb the ceiling

I had to climb into our old loft. In the 200 years since it was sealed, Mr Woodworm had been busy, and two of the hazel trunks that comprised the roof beams had collapsed. Also, I needed to spray the whole loft to exterminate Mr Woodworms' descendants.
And lay insulation.

So I cleared the room, and Acrowed it, with scaffold boards and padding on top of the Acrows. This took the weight off the flimsy joists and transferred it to the floor, thus obviating cracking. But it was a one-off, and I shall never be going up there again.

You could insulate what you can reach by leaning through the hatch. Better than nowt.

Btw, you were wise to wait a year. Too many owners rush into changing their houses before they've learned how to live in them.

Ivor