16thC listed building

[jpadie]

Hello all

I've got an oak framed brick and daub filled cottage in Surrey.  In the upstairs rooms it's difficult to get the room temperature above 14C.  One bedroom for example has two external walls and a partly sloping ceiling.  Heat cam suggests that there is no insulation in the sloping part and that the heat loss through the walls is significant. The windows are leaky and thin but small.  

 

The oak joists and beams are wider than the wall and extend inside.  I was thinking that I could chip off the plaster on the inside and then replace with foil backed PIR and plasterboard to the depth of the oak.  I'd get perhaps 75mm but there would be no air gap. 

 

For the sloping roof I'd need to take the existing plasterboard down, fill with batts and replace.   

 

My concern is whether I'm setting myself up for a later problem by not having an airgap.  The advantage of the PIR and plasterboard is it's removable and doesn't damage the fabric of the protected building.

 

Thoughts and comments welcome.

[SteamyTea]

Your main problem is going to be moisture control though the building fabric.

This will quickly lead to a lot of expense.  You may be better off, financially, just finding a way to heat the interior as cheaply as possible, which will probably mean a heat pump and forced air.  Really just a matter of how well you can hide it all.

[jpadie]

2 hours ago, SteamyTea said:

Your main problem is going to be moisture control though the building fabric.

This will quickly lead to a lot of expense.  You may be better off, financially, just finding a way to heat the interior as cheaply as possible, which will probably mean a heat pump and forced air.  Really just a matter of how well you can hide it all.

Not sure whether historic England would accept heat pumps.  They're even having to think about how UK power can upgrade the supply, even though there is an existing hole (in a window frame) for the current overhead cable.

 

Re moisture control, is the issue that there will/may be condensation in the interstitial layers of the wall?  Or that the moisture from humans won't have a way to escape once the walls are better sealed?  

 

If the latter then does it help that the windows are still leaky (such that there is rarely condensation on the windows)

[SteamyTea]

2 minutes ago, jpadie said:

Not sure whether historic England would accept heat pumps

Why I said it is a matter of hiding it.

 

3 minutes ago, jpadie said:

Re moisture control

All a bit of everything.

 

Generally, the air inside a building is at at higher temperature, and a higher relative humidity than the air outside.

To counteract this, a vapour control layer is fitted inside.  This is just a vapour impermeable layer (a bag) that stops the inside air migrating though the building structure where it may condense and cause mould.

The inside air is them mechanically pumped in and out, in a balanced manner.

 

It is really a matter of how well you can do that.

 

The only real alternative when it comes to insulation is to use a breathable insulation.  The idea being that moist air can easily travel both ways depending on temperature and humidity differentials, as well as air mass movement , but this will need to be thicker for any given U-Value.

 

By keeping the internal temperature high, the structure is also heated in a poorly insulated building.  This keeps the structure above the dew point, hopefully, or at least allows for relatively fast drying if damp occurs.

 

[jpadie]

Thanks.  All useful thoughts.   I wonder whether the fabric of the building needs to stay slightly moist to keep from failing?  For more than 500 years it's stood either absorbing or letting pass all the moisture from the straw, animals and humans that have been its denizens.   Daub does seem to be a material that can breathe.  

 

It's odd that the timbers are exposed too.  That's can't have been the original intention of the builders as surely it would reduce the overall longevity and performance.  I'd guess they were expected to be rendered/plastered over and at some point perhaps in the 19th century people decided that it looked quaint to see the timbers.