Insulating the floor of an old stone cottage

[mcna]

I’m renovating an old stone cottage in North Wales and I wish to upgrade the insulation as much as possible and I’m planning to use more natural materials in order to allow the house to ‘breath’.

 

The place seems to have suffered with damp in the past as there is a strong smell of mildew. I believe this may be to do with the fact that the place was renovated in the 70’s with cement render on the external walls, cement pointing to the stone work. Cement/ plaster internally and concrete floor slabs with no insulation (but it does have  a plastic sheet under the slab).

 

The roof needs to be stripped off completely, re-slated and timbers replaced, so I’m planning to use wood fibre insulation sarking over the new rafters with either wood fibre or wool between the rafters.

 

The walls (about 600mm thick) will have all the cement render/ plaster and pointing hacked off and re plastered with Lime. I may also fix wood fibre board internally.

 

With the floor, I would like to insulate the floor and have UFH and am prepared to break up the existing concrete to lay new floors but have read conflicting advice on how to proceed.

 

Some claim that an old stone building should have a breathable floor so that moisture from the ground is not pushed into the walls.

 

Whereas elsewhere i have read that a modern floor (DPM, insulation & concrete) will be better as it prevents water vapour entering from the ground through the floor which will create internal humidity.

 

I am far from an expert on the matter and am seeking to learn more. If anyone has experience in this area I would appreciate all comments. Thank you

 

[Cpd]

Will try and comment later as I have done similar,

try and have a search on the forum for relevant posts 

the green building forum has some great info link below

https://www.greenbuildingforum.co.uk/

 

put some photos up of the house and surrounding land as they will help to understand your environment, ie top of a hill - bottom of a bog..... and we all like photos! 

[nod]

Make sure your walls are free from damp before applying lime render 

It can act like a sponge 

[scottishjohn]

A guess on my part 

the walls will not have a damp course in them and no doubt rubble infill 

so they will act like a sponge and suck moisture up from ground 

 and if roof is not good ,maybe water going down into walls from there as well

 

 

Edited February 20, 2020 by scottishjohn

[Conor]

Hi. Unwanted opinion:

 

Knock it down and rebuild it to modern standards with revalimed stone used to face the external walls. Cheaper and building will perform much better.

 

 

*Runs away*

[scottishjohn]

I was wanting to say that  LOL

[mcna]

1 hour ago, nod said:

Make sure your walls are free from damp before applying lime render 

It can act like a sponge 

 

The cement render inside and out has been hacked off already. And will probably be a few months before we get to replacing with Lime based render/ plastering.Hopefully enpough time to dry (if it ever stops raining in N Wales!)

The roof is being completely renewed and will have all new guttering etc and as best as possible external ground levels will be lowered and have French drains installed. The walls and roof should be 'breathable'

 

The walls dont have any dpc, they are just laid directly on the ground....

[Mr Punter]

1 hour ago, Conor said:

Hi. Unwanted opinion:

 

Knock it down and rebuild it to modern standards with revalimed stone used to face the external walls. Cheaper and building will perform much better.

 

 

*Runs away*

 

I have seen this happen a fair bit in France.  Much better results than trying to fix something which is inherently defective.

[ProDave]

The only way to insulate a floor is dig it up and re lay from a lower starting point to give room to add insulation, or build up insulation on top but that will reduce the room height, which might already be low on an old cottage.

 

If digging down beware you don't undermine the possibly very shallow wall foundations.

 

Re the roof, if overboarding with wood fibre sarking, do it properly and make it a proper warm roof, with the air tight / vapour control layer on the under side of the rafters so making the whole loft space inside the heated envelope.  This is one detail you can easily get right when re roofing.  It completely avoids the need to ventilate the loft space and will eliminate the source of so many draughts.

[Cpd]

So I ripped up my old floor in my cottage and dug down to my desired depth (wish I had gone deeper....) 

the ground / earth was very solid and compacted by this time and I got it nice and level. 
I then dug a trench from one gable end to the other with a slope on the bottom towards a central trench that went out the front door which was in the centre  of the house.
‘I then graded the surfaces  on either side of the trench down from the stone walls to the centre trench so that any water would flow towards the drain and then make its way out of the house. 

i then put perforated drain pipes in the bace of the trench and filled with pea gravel and golf ball sized stones (railway rubble) 

I then put clean railway rubble across the whole floor 100-200mm deep (deeper in the middle because of the sloping bace) and compacted this in layers and capped it all of with concrete

i left an exposed 50mm gap round the side (no concrete)  

then I put down two layers of heavy duty DPC and topped the whole lot with 100mm concrete again leaving a small gap at the edges. 
I have not put down the insulation as of yet but have only room for 90mm PIR and then an under floor heating system from WUNDA 

then final floor coverings 

 

there is absolutely no damp rising up the walls, they are bone dry

 

they are 700mm thick double stone with rubble fill. 
 

I have put vent holes on the outside at the bace of the walls to help with ventilation and they are also vented at the top.

 

i have repainted the whole house with a weak cement, lime, sand mortar and not the traditional lime mortar......shock horror! 
it’s working great. 

the outside is painted white with masonry paint.

 

given my time again and knowing what I do now - against what I knew 7 years ago, I would have knocked the whole lot down and started fresh, 

 

this would have resulted in a much better house, bigger, cheaper and a whole lifetime less work.

 

however I am where I am and hopefully one day I will get it finished.......

i forgot to mention the huge underpinning job I needed to do to keep the height...........