Damp, insulation, and a 1600 Farmhouse

[Alex F]

Hello,

I have a 1600 century granite farm house in Guernsey which I have internally strip out and entirely exposed the walls and ceilings.

The walls are Guernsey granite with earthy, straw mortar. The floors are in one of the three ground floor rooms that have been stripped, hardcore and a thin hollow layer of concrete, and the other two a thick bed of sand with hefty joists and floor boards on top. The joists are rotting at the bottoms but still plenty of stong wood left.

The property appears to have had work done included some dry lining probably 40 or so years ago.

There is some wet rot around woodwork in or next to the granite walls, and at floor level. There is also death watch (is that how you spell it?)in some of the joists, lintels and beams but most appear still solid and salvageable.

I have sort initial advice of a local surveyor and a timber treatments and damp firm. An I have also spoken to a local chap who sells lime products and read a bit about the benefit of lime products.

I have established that there are two differing attitudes on how to deal with damp with regard to old properties.

The surveyor and timber treatments men are singing from the same hymn sheet. They verbally have said remove all existing wood from the walls/joints (and recommend removing the wood lintels - most not original) apply sand and cement mix combined with special chemicals to deal with the salts, and coat the walls from floor to ceiling. They are then saying Vandex about 2 foot high, all the walls. Then apply thermo board to the external walls (directly) and I think dry line the internal walls.

With regard to the floor, break up the cement floor dig, put in damp proof course and 4 inches of concrete and batten. Batten to reuse the existing wide floor planks.

The lime chaps says just apply lime directly to the walls but possibly if I want wood floors it is a still worth puting in a damp proof course in the floor.

I realise the difference in the two is one is trying to stop the damp/condensation and one is allowing it to pass through the property. It seems to make sense to me to do a method which is more in keeping with the age of the building and not to fight the natural elements and push the problems else where.

However I am concerned about the warmth of the house. As part of the works I am putting in central heating. The house is quite cold due to the way it faces I think and I had wanted wanting decent insulation to retain the heat. I realise you can use hemp with Lime but is there any thing else comparable with thermoboard?

Assuming I do put a damp proof course in the floor and rely on just lime plaster on the walls Should I do anything else to deal with damp (rising damp). In one room I was going to put some wood panelling up to hip level for example.

Would the method recommended by the surveyor and damp treatment man most likely lead to other problems?

If I put new oak lintels in and use lime plaster on walls should I still treat all the woodwork?

It also bothers me that the lime plaster method is not the conventional method recommended by the surveyors meaning it effects the value of the house ultimately, although I am planning to live in it and not sell.

The antique bronze electrical sockets and switches I have purchased from Forbes and Lomax need 45mm deep boxes. That is another possible problems in just applying lime to the walls with less depth to play with.

I would appreciate any advice on this matter.

Alex

 

[David Q]

Normally the answer from most people on this forum would be short and sweet. However normally the stone used is porous and breathable. In the case of granite, it isnt. So if the walls are already non breathable the only means for condensation to leave is via the mortar (which will breath). I suspect that the rot is because the building has been unoccupied rather than damp coming through walls. If so then lining and coating would be counter productive and could actually make things worse. All the things suggested along these lines are anathema to the idea that damp needs to move.
For my view, repair / replace rotted wood where it occurs, but try to get ventilation and heating in the property as soon as possible. Dont consider the lining / coating. All it will do is make the property as breathable as a plastic bag, and you know how damp things behave if kept in a plastic bag. Look forward to all the related comments!

 

[Penners]

The surveyor and timber treatments men are singing from the same hymn sheet. They verbally have said remove all existing wood from the walls/joints (and recommend removing the wood lintels - most not original) apply sand and cement mix combined with special chemicals to deal with the salts, and coat the walls from floor to ceiling. They are then saying Vandex about 2 foot high, all the walls. Then apply thermo board to the external walls (directly) and I think dry line the internal walls.

Good grief - where to begin?

Firstly, you give the impression that the timber in the building, albeit a bit rotted on one or two surfaces, is massive and far from beyond use. So why on earth would these experts want you to rip it all out? The deathwatch beetle will probably decide to move out once you've got the building dry (they like damp wood, not dry). And when the timber is dry you can assess how much of the surface is too crumbly to leave as is. Even then, you can repair, rather than ripping out.

If the "hefty" floor joists are a bit damp/rotted on the underside, is the under-floor cavity well ventilated? If not, this is presumably easy to rectify with air bricks or vents. Do they actually rest on the sand bed? If so, I would be inclined to dig some of the sand out, so that they are suspended with plenty of air circulating around them.

As to the wall treatment, I'm staggered at the recommendations! They want you to cover all the walls with a waterproofed cement mortar, then apply a tanking treatment internally, line the exterior with an insulation board and dry-line internally?!! :shock:

You haven't actually mentioned whether the walls are damp or not. If they are, then (noting that you intend to install central heating) I suggest that this is due at least in part to a lack of heating. Granite (as David has said) is impervious, so the only major sources of damp can be the mortar, leaks or condensation.

You can obviously look for leaks, bad guttering, bad flashing, high ground levels, and so on. If the mortar itself is wicking water in, then external repointing with lime mortar should sort that out.

And once you've got heat in the building, and thoroughly warmed it up, then condensation shouldn't be a problem. Lime plastering internally should also help to prevent damp air from condensing on the granite.

How thick are the granite walls? If you still feel that they won't keep the house sufficiently warm, then you could dry-line internally with insulation (and an air gap) behind your dry lining. But I suspect that getting the building dry and lime plastered will make a massive difference to your feeling of cold.

Hopefully some of the lime experts on this forum will also comment.

 

[Alex F]

thanks for your comments.

Hi Penners - Generally the wood as a whole is not in bad condition. They are not suggesting I rip out all wood (not floors and joists necessarily) but were recommending strongly to remove all the all wood fixings/wedges which were are imbedded in the mortar in various areas such as particularly around the doors and window and also the lintels. I believe reason is supposed to be because without the ventilation this may trigger dry rot which could quickly spread under these new conditions. The death watch at the end of one major hardword beam they would like drill test for hardness which seems sensible. I think their main objective is to seal off the damp entirely and acknowledging the knock on problems this may have they want to eliminate as much wood from the fabric as possible. Is seems to be a multiplier effect.

With regard to the ground floor joists on which the floor boards sit they are starting rot on the underside some worse then others. They are well sunken in and surrounded in sand and under that is clay. I not sure how long this situation would be satisfactory but would like a reasonably permanant solution, so possibly taking them up and putting a more solid base down would be best. This however is one of my main dilemas - whether to put a a DPC under the floor and whether this would have a negative effect on any other part of the house such as the walls. I was wondering what the other options are for this. It seems for exampple if you want a wood floor you cannot allow moisture through? So is the only real option stone floors or Carpet if you have no DPC?

The treatment I said they recommended was only concerning the inside walls, no work is proposed to the outside walls, althought the mortar on the main outside wall is cement rather than than lime infortunately.

The walls are damp in most places up to a couple foot high but I think no worse then a typical granite property of this age. It maybe that the fact that the outside of the buildings has cement mortar that is causing some of the problem for the damp.

The walls are very thick, mostly about 2-3 foot thick. I have lived in the house for a year and did not find the house retained heat well albeit we had an inadequate and inconsistent amount of heating in the house where as after this I will be fully cental heated.

If I dry lined wouldn't I have the same problems with ventilation or lack of?

I am very much leaning towards just lime plastering the walls and relying on the heating to be retained from thick walls. My main question now is what is the most appropriate material to use for the floor is if I want to reuse the floor boards and in the other room have carpet? Should I go for a DPC or breathable floor? What are the breathable floor options?

Thanks for your comments and advice.

Regards

Alex

 

[Gervase]

Alex,

Withough seeing the property all I can do is offer suggestions based on what you have stated above, but I would urge you to ignore the advice given to you by the surveyor, the damp 'specialist' and the local builder.
What they suggest would do nothing to alleviate any damp problem, and would probably make matters worse.

You are absolutely right in that the building needs to be able to breathe in order to deal with moisture. Although the walls are granite, they will be breathable to an extent, with the earth mortar between the stones providing a channel for moisture. The fact that the exterior has been pointed with cementitious mortar isn't helping, as any moisture entering the rubble core of the wall has only one way to go, and that's through to your living area - the channelling being effectively just one way!

And, as Penners suggests, do ensure that all other possible causes of damp are dealt with - leaky gutters, ground levels too high, poor drainage and splashback from concrete paths being but a few. Once treated with lime inside and out, and with other factors tackled, your walls should be dry. And dry walls are warmer walls.

If you want to have timber floors it is essential to have a free circulation of air around the timbers. Resting them on sand or clay is not advisable. It may be better to excavate the floor to a sufficient depth to build shallow stone or blockwork 'sleeper walls' topped with a DPC on which your floor joists can rest. You would need to provide some means of ventilating the underfloor space to the outside world, which could involve some core-drilling through the granite walls. The air only needs a matter of inches in which to circulate, however.

As for insulation, I'm not sure where Guernsey stands with the current building regs, but if you have a local conservation officer, now is the time to talk to him or her. Depending on how much work you envisage carrying out, you may be liable for the full implementation of Part L, which can be drastic if applied over-zealously by building inspectors.

In my view a massive granite wall lined with three-coat haired lime plaster is pretty darned effective. And, when coupled with the smaller windows invariably found in a 17th century house, and with super-efficient modern loft insulation and the latest condensing boiler, I'm confident you would have ammunition enough to take on a building inspector who wanted you to dry-line the inner walls and tack on two inches of plastic foam.

The deep sockets may be a problem. Granite is tough stuff, and chasing out for those sockets will require some specialist equipment.. Could they be mounted lower on the wooden panelling instead? Did I mention the panelling? Sorry - provided you have either a breathable floor or a ventilated floor, a breathable wall and some ventilation between the wood and the wall, there's absolutely nothing wrong with panelling.

The important thing is not to feel overwhelmed by the place or to be browbeaten by 'experts' (including us here!). If at all possible. engage the services of someone who does know old buildings and get them to look at it 'in the flesh'.

And, as I said earlier, ignore the twaddle from the surveyor and the damp 'specialist'.

 

[NT]

Dry rot needs a copious amount of water, so there is no need to worry about it unless you have water running in from the roof, a broken pipe, etc

Thick stone walls have very poor insulation values. Now is an opportunity to insulate them.

To deal with the damp you'll need at least one side breathable, if not both. So external pointing should not be cement.

For a wooden floor to work you need one of 2 options:
- ventilaion underneath the floor and the joists, which you dont currently have
- insulation and dpc to avoid condensation

Whichever way you redo the floor, I would consider insulation. Suspended wood plus ventilation will help dry teh walls below floor level, whereas concrete would trap any water content and prevent evaporation.

Damp is rarely rising, this sounds more like condensation. Tanking will not help prevent it, but will prevent it evaporating away.

45mm for electricals is not a problem if insulating, unless you want especially thin insulation. If so, using a wood backing plate (holesawed) can help bring up the required depth.

Damp 'specialists' are mostly just salesmen.


NT

 

[Matt Green]

recommending strongly to remove all the all wood fixings/wedges which were are imbedded in the mortar in various areas such as particularly around the doors and window and also the lintels. I believe reason is supposed to be because without the ventilation this may trigger dry rot which could quickly spread under these new conditions.

Just to echo NT: That's scare mongery of the highest order.


Matt Green

 

[Alex F]

Thanks for more advice.

Ok so ideally as the outside wall is seal with concrete mortar it should be hack off and repointed with lime to make as least this side breatheable and to stop trapping water in the wall.

With regard to insulation it is not an issue of building regs but more my own desire for reasonable heat and energy conservation as well as comfort. It's a fairly large family house which is the reason for my concerns over the insulation.

NT- you say "Thick stone walls have very poor insulation values. Now is an opportunity to insulate them". What would you recommend insulating the walls with. Are you more supportive of tanking and drylining or tanking and thermoboard, providing the outside wall was correctly repointed or or to make it breathable?

What sort of insulation would you use on the floor with DPC, and with the suspended wood floor. I don't have a lot of height and am already having to dig down a fair amount.

Alex[/img]

 

[middi]

There has been a lot of valuable advise and comments made already.

Unfortunately it appears that the emphasis on these type of buildings, when original constructed, was that it would never fall down, keep the chill out with a fireplace or two, and leave it to its own devises.

Mr know it all comes along and starts to interfere with it, because he wants to be kept warmer and drier than his predecessors. Nothing wrong with this.

What he does do wrong in the process, and aggravate the situation, is the slapping of tons of concrete render inside and out in the mistaken belief that not only the building will be even stronger it will be warmer too.

Any balance which existed between natural wet and dry cycles has been destroyed, the end result is one of two extremes.

1) ........The cement render externally is done at such high standard that no moisture will ever permeate it ( highly unlikely !!!!), therefore keeping the weather out.

2)....... As weather finds its way behind the hard render ( more than likely !!!) it will take an eternity to find its way out, which is usually within a nice sealed warm room.

Presented with the same situation, and willing to keep as warm as possible same as anybodyelse, My philosophy would be to hack all the hard render off, repoint in lime mortar, dry line and/or treble lime render the internal walls ( dry lining keeps more heat in ) as Gervase suggested, then if any moisture insists on finding its way in, it can bu***r off the same way it came in when the wind blows or the sun shines.

 

[Alex F]

The timber and damp chap is currently at my house preparing a full report of recommendations, about the proposed idea of simply using lime plaster on the granite walls. He is suggesting (with conviction) that if I do that without any tanking and chemicals to address the salts that will the drying out of the walls, the introduction of central heating the salts will make the lime plaster look 'horrendous'. He says the vandex tanking is breathable but prevents water, moisture not air passing through.

Very difficult to know what to do with all conflicting views. Although I am gaining a better understanding for me to make a decision independently.

By the way how do you attach pictures?

 

[Matt Green]

Water evaporating through lime plaster and leaving effloressent salt behind will not look that attractive. The salts are easily removed with a stiff brush, however, and once the wall is dry, beathable decorations will stay on the wall and look fine.

If the water is sealed in, it will rise over the vandex and give you a nice line of spoiled decorations at about 1m up the wall. Alternatively, it will break down the plaster at low level or disbond it from the wall. I would suggest those are more difficult problems to address in the long term.

Have you determined why these walls are damp? If so, have you stopped the source? If not, this entire discussion is moot.

Incidently, are the Deathwatch beetles attacking or oak/elm or pine (softwood) timbers?


cheers,


Matt Green

 

[Nemesis]

Pictures:

See my post here...

http://periodpropertyshop.co.uk/phpBB2/viewtopic.php?t=6705&postdays=0&postorder=asc&start=0



I'm no fan of dry lining, unless absolutely necessary. It robs a building of character.

 

[NT]

I'd look at removing the exterior render for 2 reasons
1. it allows the walls to dry out
2. Due to 1 it allows the fitting of interior insulation.

And 3. with hard granite your likelihood of being able to remove it without any damage is much higher than with eg soft brick.

Hopefully the walls will look good, but if for some reason they look awful and arent tidyupable, exterior insulation plus lime render would be a good way to go.

A large granite house would cost a small fortune in heat. Insulation, either inside or exterior, is going to save you money in the end. As Nemesis points out, whether there are interior features would help in making the decision re interior or exterior.


> What would you recommend insulating the walls with. Are you more supportive of tanking and drylining or tanking and thermoboard, providing the outside wall was correctly repointed or or to make it breathable?

Tanking is no part of the solution imho. You've already got it tanked on the outside, and are having damp problems as a result of this evaporation path being blocked. Your concrete floor is also effectively tanking for the underground part of the wall, preventing evaporation there too.

If the exterior is insulated, it can be lime rendered over.
If the interior is insulated, it can be drylined or wet plastered in lime for much more solid walls.


> What sort of insulation would you use on the floor with DPC, and with the suspended wood floor. I don't have a lot of height and am already having to dig down a fair amount.

Probably polystyrene under concrete, or rockwool under wood. But others might have better suggestions on that one.


NT

 

[Nemesis]

I live in a large sandstone house - it doesn't actually cost a small fortune to heat!

I certainly wouldn't start with dylining - there are other means of trying to retain heat (decent loft insulation?) before doing something which in general looks - well, crap in a period building.

And as for a solid floor - I'd avoid any DPC and look at Ty Mawr's lime flooring.


http://www.limecrete.org.uk/limecrete_info.html

 

[Alex F]

I had a picture on my PC so I have posted here to give a bit of an idea what you are discussing. This is the front elevation.

Have you determined why these walls are damp? If so, have you stopped the source? If not, this entire discussion is moot.

Incidently, are the Deathwatch beetles attacking or oak/elm or pine (softwood) timbers?

I have not determined the reason why the walls are damp but it seems to be a bit of a given (basically discussing with all different people including now a local lime plaster contractor). It seems to be accepted as rising damp. The walls have been stripped for about 10 days now and are mainly dried out but lower down in some areas more than others the clay mortar is damp. It is not worse on the front external wall which has been repointed some time ago in cement and rendered in cement at the base. The levels are possibly slightly higher outside. The worse areas of damp are on the internal walls.

I have a well about 20 ft away at the back of the house in the old conservatory. Drainage seems ok. Guttering fine. I don't know precisely what is under the property.

Regarding the death watch it is oak it has attached. But there is also some joists which I had thought were old pine which have large worm holes. I understand they only go for oak.

NT Quote: "45mm for electricals is not a problem if insulating, unless you want especially thin insulation. If so, using a wood backing plate (holesawed) can help bring up the required depth".

Three layers lime plaster would be about 35mm. So I need to go deeper which means cutting into the stone to fit the electrices or plastering thicker just around the switches and sockets which I don't want to do (defeats the object of buying flat plate switches.

My dilema and uncertainty re the lime plaster is mainly the insulation issue, so perhaps incorporating some dry lining would be a good idea. Seems to be best if I can maintain reasonably constant heat in the property to reduce condensation and in view of the time it takes for thick granite walls to heat up.

[/img]
[Open Image] [Hosted by PhotoGalaxy.com]

 

[Nemesis]

Is the house listed? It would seem a prime candidate...

We keep our house heated (low level) and ventilated and don't have a particular damp problem. The interior walls dried out well once we removed the palstic covering from the flagstones and ensured that wooden floors were actually ventilated underneath.

Removal of old crud such as cement and giving the place a chance to properly dry out is a very good plan before doing anything else. It will take rather longer than ten days though!

Rising damp - it's an easy thing to 'diagnose', but it's actually not as common as those diagnosing would suggest.

And join SPAB, buy some of the technical literature, and go with the simplest and most traditional solutions. Try too to retain as much original fabric as possible, not rip and strip out everything!

Modern materials and period buildings in general don't go well together.


http://www.spab.org.uk

 

[Alex F]

It's not listed strangely enough.

Thanks for the info.

I am certainly keen to retain as much of the original fabric as possible.

Alex

 

[Matt Green]

I have not determined the reason why the walls are damp but it seems to be a bit of a given (basically discussing with all different people including now a local lime plaster contractor). It seems to be accepted as rising damp.

Follow up question: why is damp rising in your wall? Is the external ground level less than 140mm (6") lower than the internal floor height? there has to be a reason for it- it wasn't built to have rising damp and it doesn't magically happen, there has to be a cause.

Regarding the death watch it is oak it has attached. But there is also some joists which I had thought were old pine which have large worm holes. I understand they only go for oak.

They are predominantly found in hardwoods, particularly oak, true. The reason for the enquiry, though, is that they seem to be diversifying into softwood with more frequency in the channel islands (based on the small number of surveys we do out there and annecdotal evidence in support). It seems they are capable of living in softwoods, they just preferentially select oak. Now, why they do that, we don't know.

Sorry, very geeky stuff. Just trying to keep tabs on it.

Cheers,


Matt.

 

[Nemesis]

No, that's not geeky, that's interesting!

 

[Alex F]

Follow up question: why is damp rising in your wall? Is the external ground level less than 140mm (6") lower than the internal floor height? there has to be a reason for it- it wasn't built to have rising damp and it doesn't magically happen, there has to be a cause.

Sorry, very geeky stuff. Just trying to keep tabs on it.

Cheers,


Matt.

It is interesting because that probably explains the case in the pine joists I have.

Regarding the rising damp. Yes the the external ground level less than 140mm (6") lower than the internal floor height. I don't know where the damp is coming from precisely, what I know is the walls are damp from the base up to about 2 ft and that the rear walls which are not external walls are worse in places then the front external wall (which is repointed in cement). When I have asked the question on site to various people they just say - oh yes it's rising damp. So yes lot of people I have come across do talk about it as if it happens by "magic" or automatically if there is no DPC.

Besides the fact that the levels are not ideal which seems a fundamentally difficult issue to overcome (without trying to tank), I will, following your prompting, investigate the general drainage issues surrounding the property more as perhaps the drainage is not so good in places and this is making it worse. However it is not obvious (to me at at least) that the existing drainage is unsatisfactory and ultimately the problems that should be addressed.

Thanks for your comments I will look into this question of the root cause and my drain surrounding the house.