Renovation advice for stone croft house

[MMeNDtal]

Hi all! I hope this is the correct place to post this. I introduced myself on the forum yesterday and got some helpful advice on my project, but figured I should write up a proper post in the correct forum.

I have a stone (rubble) house in Shetland that has been largely untouched since it was built, over 100 years ago! We've gutted the upstairs, in preparation for new stud walls / insulation.

My question is, what setup will work best on such a building, which originally relied on the heat inside the house soaking through the stone walls to prevent condensation.

What's been suggested so far is something like this:
STONE WALL - AIR GAP - TIMBER FRAME WITH INSULATION - AIR TIGHT MEMBRANE - 25MM BATTENED SPACE (for services) - PLASTERBOARD

My question is, with this setup, would I need to install a few vents through the stone walls of the house, to ensure air circulation?

Alternatively, would roof vents through to the loft be enough? Or a breathable roof membrane (we plan to redo the roof anyway)?
Would I also need some sort of vapor barrier on the stone wall side of the timber frame, or is that not necessary?

Additionally, you can see in the second picture that the stone walls are built into the slope of the roof. I removed a layer, to access a few rafters that needed replacing. The boards behind the stone were moist. They've now dried out, so I assume it was condensation. I can't really see any reason for the stone above the level of the wall plate, so would it make sense to remove everything down to this level to help the wall breathe?

Thanks for any advice!
 

[nod]

A 50 mil metal stud would work perfectly 

[scottishjohn]

looks like its been repointed with cement and not lime  assuming ouside is done the same --so any water will sit in wall and not evporate out 

 ideally rake out outside and redo with lime at some point

 50mm studs in metal ?

I presume  you want to keep room sizes as large as possible 

140mm of normal studs and insulation will take alot of floor area away --and thats what you would need to get to modern spec

then  i would build  small wood frame or metal studs and use CLOSED cell spray foam --not cheapest --but best R value  for thickness and totally water proof  and will stick inside framing to outside as well - leave it shy of top of studs --so you have a complete hard skin --then fill  with what ever after that or foam backed PB --40mm is minimum I think you will find for water proofing 

 If you do the back of the sarking boards as well you will have it air tight as well 

often used as the water barrier in basements  on the outside  in US

 check it out your self 

Edited March 8, 2020 by scottishjohn

[scottishjohn]

1 hour ago, MMeNDtal said:

My question is, what setup will work best on such a building, which originally relied on the heat inside the house soaking through the stone walls to prevent condensation.

they relied on lime mortar to allow walls to breath and probably lime wash on inside or lime plaster 

[scottishjohn]

1 hour ago, MMeNDtal said:

Hi all! I hope this is the correct place to post this. I introduced myself on the forum yesterday and got some helpful advice on my project, but figured I should write up a proper post in the correct forum.

I have a stone (rubble) house in Shetland that has been largely untouched since it was built, over 100 years ago! We've gutted the upstairs, in preparation for new stud walls / insulation.

My question is, what setup will work best on such a building, which originally relied on the heat inside the house soaking through the stone walls to prevent condensation.

What's been suggested so far is something like this:
STONE WALL - AIR GAP - TIMBER FRAME WITH INSULATION - AIR TIGHT MEMBRANE - 25MM BATTENED SPACE (for services) - PLASTERBOARD

My question is, with this setup, would I need to install a few vents through the stone walls of the house, to ensure air circulation?

Alternatively, would roof vents through to the loft be enough? Or a breathable roof membrane (we plan to redo the roof anyway)?
Would I also need some sort of vapor barrier on the stone wall side of the timber frame, or is that not necessary?

Additionally, you can see in the second picture that the stone walls are built into the slope of the roof. I removed a layer, to access a few rafters that needed replacing. The boards behind the stone were moist. They've now dried out, so I assume it was condensation. I can't really see any reason for the stone above the level of the wall plate, so would it make sense to remove everything down to this level to help the wall breathe?

Thanks for any advice!
 

hope thats an old picture cos plenty of damp to rot things showing there--you can see wall is full of damp,by clour of old lime mortar --

I,m guessing it would have no damp course and probably ground floor was beams sat on bits of slate above the earth-

so whats been done to make floor damp proof-new slab and DPC?

Edited March 8, 2020 by scottishjohn

[ProDave]

5 minutes ago, scottishjohn said:

they relied on lime mortar to allow walls to breath and probably lime wash on inside or lime plaster 

Most that I see are lath and plaster on the inside (with no insulation between that and the stone)

 

From what I hear "plaster on the hard" was only done by poor people.

[scottishjohn]

2 minutes ago, ProDave said:

Most that I see are lath and plaster on the inside (with no insulation between that and the stone)

 

From what I hear "plaster on the hard" was only done by poor people.

to work CORRECTLY lathe and plaster needs a gap up the wall and air flow from under floor into roof  space or out at eves 

Edited March 8, 2020 by scottishjohn

[Cpd]

4 hours ago, MMeNDtal said:

I can't really see any reason for the stone above the level of the wall plate, so would it make sense to remove everything down to this level to help the wall breathe?

it’s very likely that this additional stone is there to stop the roof blowing off ! You will probably find that where the roof joist fixes to the wall plate there is considerable rot in either the wall plate or the joists or both and that the actual fixing strength at this point is long gone. The additional stone will really help to secure the roof from up lift. Before the use of wall plates there would have been timber crucks ( lengths of large timber built into the stone walls) attaching the roof to the walls and stopping the roof from blowing away. You can remove this additional stone but you will need to add one or even two rows of noggins to strengthen the bottom of the joists and then LONG metal strapping attaching every joists to the wall. This will let the timber joists breathe better and also prevent your roof blowing away..... remember not to pull all the stone work away in one go, do half a dozen at a time so that the roof is never vulnerable if the weather changes..... it happened to a friend who did this exact thing while replacing a roof of similar vintage, new tin , tidied up wall heads, big wind and whole roof was on the lawn next morning. I am not an expert so do your own cross referencing.

[Cpd]

4 hours ago, MMeNDtal said:

Alternatively, would roof vents through to the loft be enough? Or a breathable roof membrane (we plan to redo the roof anyway)?

I installed  4 roof vents high up which will all help in keeping the air circulation high, my loft is only a small triangle that is below the ridge beam so I wanted as much air flow as possible.
All the 50mm gaps below the sarking and between the rafters all vent into this space as do the soffit vents. You can really feel the air movement in each and every rafter bay. 

a roof membrane is a must as it’s your second line of defence if you get a leak, it will lessen air movement and this is why I put soffit vents In linked to the vented ridge area. 
I really went overboard on venting the old parts of the building but it’s working a treat. 

[Cpd]

Roof vents from the outside and the vented area below the ridge just before we cover it over with 250mm of PIR from below. 

[Cpd]

4 hours ago, MMeNDtal said:

we plan to redo the roof anyway

I think you mentioned this before and talked about replacing with slate...... I would strongly suggest you replace with corrugated iron or box profile or something light weight  as the additional weight of slates on a roof like this may well cause structural issues......  it may have had slate on once but that was a long time ago and the timbers are now well past there best before date.... I expect with a little tlc the timbers will last another 100 years,  I have worked on buildings like this where we ripped of the the first 6 foot or more of the sarking so that we could inspect all the joist ends, replace as needed and treat all the old ones and in one case replaced the wall plate  without pulling the whole roof off.... 

[MMeNDtal]

On 08/03/2020 at 17:24, scottishjohn said:

hope thats an old picture cos plenty of damp to rot things showing there--you can see wall is full of damp,by clour of old lime mortar --

I,m guessing it would have no damp course and probably ground floor was beams sat on bits of slate above the earth-

so whats been done to make floor damp proof-new slab and DPC?

The rotten rafters and tie beams have been replaced. The roof is leaking in a couple of places, which we only discovered after ripping out the internal walls (it looked fine in the loft space). The downstairs floor is half suspended, half slab. I doubt very much it has any DPC anywhere.

[MMeNDtal]

 

22 hours ago, Cpd said:

You can remove this additional stone but you will need to add one or even two rows of noggins to strengthen the bottom of the joists and then LONG metal strapping attaching every joists to the wall. This will let the timber joists breathe better and also prevent your roof blowing away..... remember not to pull all the stone work away in one go, do half a dozen at a time so that the roof is never vulnerable if the weather changes..... it happened to a friend who did this exact thing while replacing a roof of similar vintage, new tin , tidied up wall heads, big wind and whole roof was on the lawn next morning. I am not an expert so do your own cross referencing.

Yes, I was planning to replace the original roof straps. It looks like they're all that's currently securing the roof! Additional bracing with noggings seems sensible, too!

[MMeNDtal]

22 hours ago, Cpd said:

a roof membrane is a must as it’s your second line of defence if you get a leak, it will lessen air movement and this is why I put soffit vents In linked to the vented ridge area. 
I really went overboard on venting the old parts of the building but it’s working a treat. 

Would you suggest a breathable membrane or is that not necessary, with the roof vents?

[MMeNDtal]

21 hours ago, Cpd said:

I think you mentioned this before and talked about replacing with slate...... I would strongly suggest you replace with corrugated iron or box profile or something light weight  as the additional weight of slates on a roof like this may well cause structural issues......  it may have had slate on once but that was a long time ago and the timbers are now well past there best before date.... I expect with a little tlc the timbers will last another 100 years,  I have worked on buildings like this where we ripped of the the first 6 foot or more of the sarking so that we could inspect all the joist ends, replace as needed and treat all the old ones and in one case replaced the wall plate  without pulling the whole roof off.... 

I was thinking something like fiber cement tiles?

[Cpd]

14 minutes ago, MMeNDtal said:

Would you suggest a breathable membrane or is that not necessary, with the roof vents?

Yes it’s still necessary even with roof vents, they are cheep as chips in the big picture, just make sure you don’t use one that will become defective if it gets wet and then freezes   This happens very easily and has happened to me twice !!!!! It literally makes the roof membrane useless! There are various recommendation on this forum from people like @Crofter and I think @ProDave but you want one that can withstand wet freezing conditions if there is ANY chance of this happening while the roof is open. CHECK THE SPECS. 
 

also when you decide to take the old roof coverings of it may be a good idea to add some false rafters in your gable ends to allow yourself to build eves as this really helps to get the water away from the gable end wall heads. I’ve done it and helped 3 friends do the same and will also do it on my main house when the time comes. 

[Cpd]

26 minutes ago, MMeNDtal said:

I was thinking something like fiber cement tiles?

Sorry I know nothing about them, but if the roof can handle it then it would be a good opportunity to batten and counter batten, this would then leave you roof membrane intact without hundreds of nail holes, which happens on a traditional slate / sarking roof.