retrofit underfloor in old building

[eekoh]

So it looks like I may be going for a renovation rather than conversion / new build - there's an old house come up locally that my partner and I can afford and if we're successful at auction in Feb we'll need to get straight on with the work to minimise the time we need to keep our rented house so I'm attempting to spec & cost some of the work beforehand. (Also it'll be useful for any future project if we don't manage to get this place.)

 

Its a stone cottage over 3 floors and as it needs a full refurb it gives us the opportunity for a 'blank slate' approach to the heating system.  We're thinking of wet system UFH throughout - ground floor is partly solid and partly suspended timber (over a small cellar), upper levels are obviously suspended timber floor. Also we'd retain existing open fire (or replace with log burner) for extra 'instant' heat in downstairs living room.

Solid stone walls so everything needs to be breathable to avoid damp problems and this is the main point where I'm looking for some advice.

 

Lime (or possibly Hempcrete) seems the obvious choice for screed.

Breathable insulation materials - so far options seem to be sheep wool or plant-based fibre board (wood / hemp)

 

Does anyone have any recommendations or comments either pros or cons for any of these materials?

Wool seems to be only soft rolls rather than boards - can you fix UFH pipes to these?

Could you put lime/hemp screed directly onto wool?

Do I need a solid fibre board for the suspended timber floors to maintain the weight-bearing load? (Not sure exactly how different a screed would be compared to floor boards in this respect) 

 

Thanks for any advice / comments.

 

[Ferdinand]

Consider carefully the costs vs benefits of so called ‘green insulation’. Sheep’s wool sounds nice and fluffy, but there are alternatives available which are much more insulating per unit thickness, which means that you are trading off your ability to save future C02 emissions for a trendy material now. And potentially you will need to dig bigger holes in the floor to fit it in for X level of quality, so waste, effort, fuel etc.

 

I would suggest as a start a heat model of the( whole thing, and to include 10-25 years of energy bills and emission in your lifecycle calculations.

 

Ferdinand

[AliG]

I wouldn't recommend UFH for this kind of project.

 

1. UFH doesn't work well in retrofit situations. It can be done but it is much less efficient on timber floors than solid floors. The ground floor may be a more workable job. I would just stick with radiators upstairs.

 

2. UFH is designed for a modest low heat output. Unless you can considerably improve the insulation you will have problems. Not only may you not be able to get a high enough heat output to warm the house, but it could see large temperature variations depending on the outside temperature that UFH will not cope well with.

 

Hopefully someone can give you some help on insulating the solid stone walls. I do know that without insulation they have awful u-values, worse than a double glazed window.

 

 

[eekoh]

@Ferdinand I'm not in any way set on sheeps wool, that was just one of the most frequent things that seems to come up on searches for breathable insulation. Of the products I've seen so far I'm actually leaning more towards the hemp fibre stuff as there is a local firm that works with it and from what I've read so far its very good on both thermal and acoustic insulation.

 

@AliG

Its got 18" thick stone walls so seems unlikely to me that there would be any rapid variations from external temperatures and UFH is used very effectively in stone barn conversions so why wouldn't it be suitable for a stone house?  The constant heat output is better for keeping damp at bay than the alternating high heat / low heat, on/off approach of radiators, though I do take your point about needing to ensure a high enough heat output to warm the place adequately.

I'm also aware that a suspended timber floor is probably less efficient than a solid floor as we wouldn't be able to use the same depth of screed, though the info I've found so far on Hempcrete screed suggests that you can get good performance from shallower depth than you'd need for concrete.

 

Insulation is another aspect that I'm looking into, the whole solution will need to be a balance between heat input and insulation to reduce heat loss.  I've got a bit more investigating to do working out where that balance would be with this place. There is existing external render which I think is Edwardian (identical appearance to another local building with known materials), which would be lime based though clearly will need checking as non-breathable render would create damp problems. We'd also be using lime or hemp-lime plaster for the interior so that would contribute a bit too.

[scottishjohn]

we need to now EXACTLY how its constructed now to give best advice 

 pictures would be good 

walls --stone ,but is there then a gap and lathe ~plaster?

 how big are the rooms --how much space can you afford to loose in the rooms . -

 Is exterior insulation + water proof render an option -you kill two birds with one stone -- walls will never get wet again and can then act like a heat sink if insulation is exterior ?

also you loose no interior space ,

 so many ways --common choice for barn conversions is to spray inside of wall with a layer of  CLOSED cell foam --water proof,so damp does not get inside   then  build new stud(house inside a house 

 - no doubt old floor joist are set in walls --ends rot off --so you can move them at same time - basically TF inside stone skin ?

do alot of searching to decide best way for yuor house --no two old hoses are built the same

 

 then there s the question would you be allowed to flatten and build re-lacement -that would laways be first choice if you areallowed iif you wanting 21st century economy running costs at cheapest and definable costs before you start

 much easier and probably cheaper to do than major refurb with all the bobby traps you don,t know about till you get stuck in 

 ,so can you ask planning if it would be possible for flatten and rebuild before auction -

 

Edited December 24, 2019 by scottishjohn

[Triassic]

In the last renovation we dug out the ground floor  and filled in the cellar, we then fitted polystyrene insulation, with concrete above. We self installed  underfloor heating, fixed using cable ties, to steel mesh reinforcement. In the upstairs rooms we fitted wall radiators. I’d suggest you use modern insulation rather than sheep’s wool, as it’ll take up less space. 

Edited December 24, 2019 by Triassic

[Temp]

Has it been empty more than 2 years? If so you can get any work done by a vat registered builder at 5%. But work must start before you move in. If you move in first it won't have been empty for two years before work starts so won't qualify. There is no reclaim scheme so has to be a vat registered builder.

[eekoh]

@scottishjohn demolition is not an option, we’d want a totally different sort of plot for a new build.
From what I can see it’s plastered directly onto the stone, no sign of lathes on the bits that have broken away. Structurally seems in generally good condition, room sizes are mostly fairly big apart from box room on middle floor. From the decor it appears to have had a lot on money spent probably in the 80s but nothing much since. External (lime?) render is intact, internal plaster deteriorating fairly rapidly since it’s been empty.

 

@Triassic yep, wool is quite bulky and also fairly expensive. I want to find out more about the hemp fibre products, they look good so far. possibly still expensive tho.

@Temp it will have been empty for approx 1yr so we wont qualify under that scheme. I think we’d probably do at least some of the basic install ourselves and then contractors for the plumbing & electrics commissioned and screed.

 

 

[scottishjohn]

1 hour ago, eekoh said:

scottishjohn demolition is not an option, we’d want a totally different sort of plot for a new build

so next question is what will its resale value be after you have done all the refurb ?--

maybe its not a viable idea with out a rebuild if its not going to be worth that much ?

 full stone and hard lime plaster walls --  you will never stop the damp coming up from ground ,as there will be no damp course or poissibly even foundations 

If you keen -speak to someone whio is very familar with these type of houses in your area who has already brought one into 21st century condtion --sounds like a real money pit to me

 what size is the plot and what is guide price ?. all mains services ? or septic tank and well water

 

Edited December 27, 2019 by scottishjohn

[eekoh]

At the price we’d be buying for there would be good scope to gain on resale value later. UFH is probably the biggest cost that isn’t necessarily essential (we could reinstate the existing radiators after plastering) and the cost will be one consideration on whether we do it. What I’m looking into now with materials & specifications is to inform that decision.

The house is fairly typical construction for this area, I’ve rented 4 different homes with similar construction since moving here and several friends either have done or are in the middle of renovations so I am reasonably familiar with the issues of living in and working on stone houses.

 

The house isn’t a complete wreck and has full mains services. It would be basically habitable with a good scrub down and a skip for the old carpets, so we could do a slow & steady program of refurb room by room after we move in. But while it’s empty initially and we have cash available it gives us an opportunity to consider some bigger things (like upgrading the heating) which could make it a better home but would be more difficult to do later on.

Edited December 28, 2019 by eekoh