back pointed roof and loft conversion

[millsmum1]

Hi we are just in the process of buying an old house, which has a massive loft. I wanted to make this into a useable room. but I am now not sure on how to do this.
I would like some advice on how to insulate the loft so that we can use it as a room. the roof is in good condition and to reroof we could be looking at around 10k.

the roof is backpointed, and being in the loft the other day when it was around 2 degrees outside you could visibly see the condensation building on the underside of the tiles. I am of the understanding that we cant insulate by leaving a gap then adding the insulation then plaster boarding as the condensation will build up in the void.

we can spray foam but that seems to be frowned on

we can re roof but we don't have the budget

do we have any other options?

a couple of the bedrooms have damp issues around the chimneys which we are planning on removing but on closer inspection it could be also related to the gutters or even the build up of condensation in the loft running into the tops of the walls?

There is virtually no insulation on the floor of the loft either

any help would be really greatly appreciated

 

[vinn]

To make a loft into "a usable room" is, in essence, a loft conversion, and Blg Regs and BCO's inspections will come into force.
There's lots of recent info on here if you search.

The condensation on the torching and tiles is due to heat rising from below. Again, there's masses of info ref the subject: how to insulate your roof and loft floor etc.

The possible water penetrations or leaking gutters will need to be water tested.
Chimney stacks & chimney breasts are valuable features in a property.
All flues need sweeping and venting top and bottom.

 

[geraldthehamster]

the roof is backpointed, and being in the loft the other day when it was around 2 degrees outside you could visibly see the condensation building on the underside of the tiles. I am of the understanding that we cant insulate by leaving a gap then adding the insulation then plaster boarding as the condensation will build up in the void.

You can insulate it, in principle. The condensation occurs because warm moist air from the house rises and hits the cold surface of the tiles. This cools the air, cold air holds less moisture than warm air so the water condenses out. When insulating between and under the rafters you would fit an impermeable vapour barrier, either as a separate layer or in the form of the foil backing to the insulation board. This prevents the warm air from entering the cold space, and condensation should not occur. Ensuring a ventilated air gap on the cold side of the insulation, beneath the tiles, enables any moisture that does penetrate, from below or above, to be dispersed.

Cheers
Richard

 

[^woody^]

If the roof has torching, then it could well be at its life end, and retiling and insualtion can be done at the same time. As can passing in all the the new timbers and beams through the roof.

 

[millsmum1]

You can insulate it, in principle. The condensation occurs because warm moist air from the house rises and hits the cold surface of the tiles. This cools the air, cold air holds less moisture than warm air so the water condenses out. When insulating between and under the rafters you would fit an impermeable vapour barrier, either as a separate layer or in the form of the foil backing to the insulation board. This prevents the warm air from entering the cold space, and condensation should not occur. Ensuring a ventilated air gap on the cold side of the insulation, beneath the tiles, enables any moisture that does penetrate, from below or above, to be dispersed.

Cheers
Richard

thank you Richard,
totally understand about the warm and cold air. I am just worrying now. I originally planned to leave a 50mm gap and then add 100mm kingspan. plaster board, and plaster. on talking to the roofer he converted his loft and was still getting condensation on the otherside of his plaster which was then coming through as damp spots. as the moisture was building on the cold side. I also then am worried about the roof timbers rotting.

or am i over thinking this??

 

[geraldthehamster]

I originally planned to leave a 50mm gap and then add 100mm kingspan. plaster board, and plaster. on talking to the roofer he converted his loft and was still getting condensation on the otherside of his plaster which was then coming through as damp spots. as the moisture was building on the cold side.

Maybe he was getting cold bridging at the rafters? That's why you should have a layer of insulation beneath the rafters as well as between them.

100mm Kingspan will not be sufficient for building regulations.

Cheers
Richard

 

[Doggit]

Assuming the roof joists are 100mm, then add a 50mm batten to them, put the 100mm cellotex in between the joists, then add insulated plasterboard across the joists that is 35mm celotex+12.5mm plasterboard. Make sure that the airflow can go up and over the insulation from one side of the roof to the other - make sure it doesn't get trapped at the ridge beam.