Damp, insulation, and a 1600 Farmhouse

[Gervase]

if the difference between your floor and the outside ground is only six inches the you are gong to need some sort of french drain externally if you are to get rid of the damp,
However, 10 days is a very short space of time to observe the rise and fall of the damp - I would tell someone to wait for 10 weeks, particularly now autumn's here and condensation and humidity are skipping hand in hand to saturate everything.

I'm with you on wanting to preserve the place in as original a condition as possible, and I have a strong dislike of dry-lining; it's prescribed far more often than it's needed, and in the majority of cases, drainage is the answer. Our place has thick stone walls and is in a very damp part of the world - but we have cured any dampness by addressing the drainage and by keeping the heating on at a very low level from October through to March. It sounds bizarre, but we actually use less oil by doing that rather than have it come on twice a day at 'normal' levels.

If you want to go for panelling, what about lowering your switches to mount them on the panels - surely that would give you the required depth?

 

[NT]

Pretty house.


> I have not determined the reason why the walls are damp

that really is the key question.


> but it seems to be a bit of a given

I'm not sure what you mean there. PPs are not normally damp by design if thats what you mean.

> (basically discussing with all different people including now a local lime plaster contractor). It seems to be accepted as rising damp.

Sounds like youre talking to the wrong people. We'v had that one discussed to death on here, and from looking at the many inputs of evidence and the science behind it all I could only conclude that rising damp is a rarity. Most cases of damp bases of walls are condensation or penetrating damp. And you've got a prime cause for each of those. Ground level not 6" below floor level increases likelihood of penetrating and condensation, and low insulation stone sitting on damp earth makes the stone cooler at the base, predisposing to condensation at the wall base. Plus youve got cement down there which prevents normal evaporation.


> The worse areas of damp are on the internal walls.

sounds like condensation then.


>> 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.

Above explains you dont need to drill the granite, though that wont give you flush 45mm deep fittings. If you want flush fitting, I would simply use shallower switches. For example, take squares of sheet brass, suitably finished, and add standard mains toggle switches (half inch hole types) found in any electronics catalogue. Fit these pseudoperiod switches to modern pattresses. You wont need anywhere near 45mm. For best result you could mill the front nut down to a round shape, or thread the brass hole.

There are other options too, but its hard to suggest options without being clearer about what you want to achieve.


> My dilema and uncertainty re the lime plaster is mainly the insulation issue, so perhaps incorporating some dry lining would be a good idea.

perhaps, but you dont need dry lining to have insulation.

> 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.

no, normal heating control will minimise waste


> 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).

Right, classic signs of condensation.

> 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.

Yes, but this is more common myth than expertise. Fact is millions of PPs have no dpc and no damp problem. Assumption that lack of dpc will cause damp indicates several steps of non-knowledge re period properties and damp. In the great majority of cases all one need do is understand where modern maintenance has gone wrong and put the damp handling features of the property back to how they were intended to work, and the damp disappears. How old properties handle damp has been widely not understood for many years. There is still a lot of ignornance about it.


NT

 

[Penners]

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

Our 4-bedroom C17th Hornton stone house in Oxfordshire was probably the cheapest house to heat that we've ever owned.

Yes, massive stone walls take some heating up, but they also give off their heat for a long time after the central heating has been switched off.

 

[Nemesis]

I do tend to try to centrally heat me of course - alcohol inside and warm clothes out.

 

[Penners]

I do tend to try to centrally heat me of course - alcohol inside and warm clothes out.

I bet you can get a grant for that.

 

[middi]

Nt,s paragraph relating to the general misunderstanding of damp, lack of DPC,s, floor membranes, modern manipulation of the breathing mechanism of PP,s etc.., etc....is very very true,

I would like to add to this the fact that whlist our ancestors which built and lived in these properties may have not suffered the degree of dampness which our contemporary's are suffering in the same dwellings, it is a very stong possibility that some PP's would have been prone to damp from day one. Traditional material built, or otherwise.

Because of our expectancy in accepted modern living standards we tend to winge a lot louder than what they probably did.

Scratching our heads on this topic will then become banging our heads against the same damp walls.

"Scientific" solutions to the problems are well advertised, this kind of remedy would only work if scientifically administered. They have a role to play towards eliminating the problem if appropriate for the individual situation.

We all know that this is not the case and a lot of chemical remedies are " salesman" orientated.

It is not so much a question of understanding damp, it is more a case of understanding the PP and at what point you stop worrying about it and containe it with simple solutions.

I am of the opinion that at times we want to improve something which within its own parameters was perfect in the first place.

I agree it is not easy.

 

[NT]

Theres good science, inapprpriate science, pseudoscience, and plain rubbish. Marketing and sales will move along the path from left to right until they find one of those categories that'll help them sell their wares to (mostly ignorant) buyers. In the case of damp remedy products, categories 2 and 3 seem to be fairly common.

What is appropriate science and treatment for new buildings is not necessarily appropriate for historical builds, which used significantly different methods to handle and prevent damp.


NT

 

[Alex F]

Thanks for further comments.

The walls generally are now dry and the could not really be described as damp having been exposes to fresh air and fairly mild weather for about 2 weeks now.

I am more or less decided to go with the straightforward lime plaster method on the walls and not dryline or tank. I am keen to use permeable materials rather than physical barriers as a whole. So therefore no tanking and preferably no dpc.

Having taken up the floor boards the joists that were burried in the sand were actually rotten through in many cases. I have done most of the precess of reducing the floor levels by about 10 inches in the three rooms. Rather than a concrete floor with a dpc, I am considering a suspended floor with ventilation. I was thinking (but plan to get expert advice) of creating three concrete beams, one at each end and one in the middle, and suspending the joists to these and putting my floor on these joists and well as venting outside. Are there any major problems with this idea?

The level under the joists will be below the ground level outside. There are existing holes in the walls which pass 3/4 of the way through the external wall. They look definitely purpose made and possibly some form of drainage. Anyone Know what these are likely to be? They are about 8-10 inches below where the floor level was and about 4 inches by 4 at the opening. If I used these as the vents (which would be convenient), once I am through the entire wall I will need to go up 8-10 inches to get about ground level. How would one normally create this ventilation, ensuring water cannot access the vents? I can put a pipe through the hole, but what would one put at the end on the out side of the building?

 

[NT]

Normally that would all be built in while the wall was built. Theyre not really retrofittbale, so now its upto you to improvise.

NT

 

[Penners]

If your underfloor vents will be below ground level on the outside, then you'll need to excavate a small "well" for each of them, to prevent the earth from falling in and blocking the vent. These wells can be made from whatever you like, really - concrete, metal, plastic, etc.

To stop the wells filling with water when it rains, I would put a little roof a foot or so above each one.

 

[middi]

I suppose one could always build a short periscope type vent with drain pipes and 90 deg. bends.

 

[Penners]

To ventilate the floor and spot enemy submarines.

 

[Gervase]

Using concrete beams for the sleeper walls to support the floor sounds good to me; laid on sand they should be nice and 'dead', and topped with a damp-proof strip, they shoud keep your woodwork out of harm's way. Remember to align them so that each 'cell' created can be ventilated.

 

[NT]

Plastic drain pipe would be very out of keeping though, but could possibly be covered with something. Dont forget mesh to keep out mice.

One time I saw this done, little brick wells were used, one brick on each of the 3 sides, so the front was 2 bricks wide and the sides 1 brick deep. The bricks have to come to above ground level to prevent water runin, and need to be cleared out of leaves etc regularly.


NT

 

[SGray]

Hello. I have been following this topic with a lot of interest as we have just moved into a 200 year old stone cottage in N. Somerset which has been extensively modernised over the last decade (last house we lived in bult in 1970 so living in a pp is new to us) and have discovered damp in the sitting room, dining room and kitchen; low level, rising to about a foot, some internal walls as well as external walls. (the internal walls that are most affected are the thick stone walls that were possibly once originally external). A local architect who has some sort of conservation of old buildings qualification suggested that the problem was not too bad and could probably be dealt with by removing the skirting boards (which are green and mouldly behind) and leaving a gap between the floor and the wall!? (a damp proof course covered in concrete has been laid in recent years on the floor internally and this is covered with pine floor boards). He also suggested increasing ventilation by leaving the windows locked open (yes, I'm really sorry to say that the windows have been replaced with pvc) which will be cold in the winter, and leaving the heating on low all winter - I note that some of you do this and don't find it an expensive way of heating your house. The kitchen would need unfitted furniture.
A surveyor who comes recommended to us by the owners of a listed pp has helped us to discover that the rain water gutters all around the cottage are emptying themselves about 1/2 metre away from the building staight into the ground, underneath a membrane that has been covered with lorry loads of gravel! The external ground levels are therefore nicely above the internal levels and keeping nicely wet! They have been like this for at least 3 1/2 years. We have started digging. Am I right in understanding that we should be lowering the external ground levels to 6" below the internal level? and when would a French drain be necessary? could we just leave bare earth (a flower bed perhaps) around the external walls?
He has also recommended tanking the internal walls up to 2 or 3 feet. When we asked him what then happens to the water in the walls (the external wall is rendered - probably a modern concrete render) he shrugged and said that they have always been wet but that tanking seems to work. So here is my next question: is there anybody out there who has used tanking as a method of dealing with damp succesfully in the long term? I know that it is not a popular method with some of you but we didn't really envisage needing to do loads of work to this house so are not quite yet prepared to try and remove and replace external render, replace internal plaster and dig out concrete floors.
One last question: might it be enough to simply get all the external digging and drainage work done around the house and how long before we started seeing results if this is all that is needed?
Let us know what decisions you come to Alex F; I have been following the discusson with interest.

 

[Penners]

AGray,

You've asked a lot of questions, and it's not really possible for anyone to give you a definitive answer as to how many of your suggested solutions will be required, in order to deal with your damp. Eliminating problem damp is always a progressive process - you try one thing, and then wait to see whether it works. If not, you move on to the next... and so on.

It sounds as though a number of things are contributing to your damp problem. Indeed, you have almost the archetypal damp property! Your internal floors have recently been concreted, thereby pushing the damp out to the walls. Your external soil level is higher than the internal floors. Your surface water is not being drained away from the building. And you have concrete external rendering. A "full house"!

In your shoes, I would take two steps immediately. I would dig a French drain around the house. Just lowering the soil level would not, I suspect, be nearly as effective as removing soil from contact with the walls and replacing it with gravel. Just make sure that you don't dig down as deep as the bottom of the foundations.

Secondly, I would sort out the bad surface water situation. Dig a proper soakaway a good distance from the house and channel all surface water into it.

Those measures, combined with warmth and ventilation, should start to have an effect. But remember that this effect won't be seen as quickly or effectively in winter as they would in summer. So I should be prepared to wait for a good 9 months before deciding whether those measures alone have been sufficient to reduce the problem to acceptable proportions.

 

[middi]

SGray,in your situation I would start to deal with the obvious before I would get too confused with remedies which involve tanking, more damp proof cement and only GOD knows what else.

Therefore:-

1)........Prime objective, 6 inches is a minimum guide line for the exterior level to be below internal floor level, one foot or more is a lot better, therefore attend to this.

2).......Make sure that all gutters are good and take ALL the rain water away from the house, minimum 5 metres, 10 is much better and preferably on a slight slope away from the house if possible.If clay type of soil, as far as you can into constructed soakaway.

3).......Attend to any void below ground floor with generous ventilation with no obstruction.

4).......Again, if clay soil or badly drained site generally, a french drain incorporating perforated 4 inch tubing if you want to, take as much as the naturally occurring surface water swiftly away from site.

Once all this is done monitor the situation for at least a summer and into the next winter and thing again then.

I think it is a bit pointless to attempt repairs and remedies untill you make sure that you have done the best you can to avoid exess water being sucked up the walls again.

 

[NT]

As Penners says really. Each thing you do to reduce ingress or improve evaporation will improve the situation. By how much is not really possible to know in advance.

Water content in walls is a dynamic equilibrium between water ingress and evaporation out. To dry a wall you prevent unnecessary ingress and increase evaporation.

Tanking will therefore make matters worse, since it prevents evaporation. It will cover the damp up nicely, but things will only then gradually get worse, until the tanking is no longer able to mask the problem.

Relatively easy things to do are reduce ground levels, remove rotten skirting, repair any cracks in the render, check rainwater goods are not discharging onto the wall, fix rain drainage, and ensure you've got adequate ventilation. Also identify interior sources of water vapour and minimise, as condensation is probably part of the problem and reducing RH counters this.

Less easy things are removing external render and removing concrete floors. Hopefully you wont need to do either, but only time will tell.

Another option is a humidistatic dehumidifier. This is more practical and cheaper than excess ventilation.


NT

 

[SGray]

Thank you NT, Midi and Penners. Waiting is a bit depressing because we have knocked away some mock sand stone facing on the chimney breast wall leaving bare plaster / concrete showing, and sanded down the floor boards (they were very dark) and so at the moment the sitting room is out of action. We were hoping to have it decorated by now. But I have taken note of your advise and we will start by sorting out the outside.

 

[Alex F]

That is the problems I have had to deal with and many others no doubt - where to draw the line. You either wait dry out and monitor, or you pretent you have no problems and redecorate and put back new skirting or you prepare for further cost strip out more redo properly.

Going back to my case and these vents using brick or stone wells seem aesthetically the best option, although the rain water would not drain as well, as it would sit and possibly pond in between the wells. It's getting complicated. Could I not just put a couple of vents in the floor itself internally.

I am concerned that this suspensed floor option with vents does not seem widely adopted as an option for a PP like this where as a DPC does (certainly here in Guernsey anyway).

There is a National Trust 15 century farm house that is being restored here which I enquired about. They are supposed to be doing it using all traditional materials. However I have learn that even they are putting a dpc in the floor which is hardly consistent with the original the build. see http://www.nationaltrust-gsy.org.gg/pages/isl_properties/lesCachesBarnProposals.html .

Not being an expert I am nervous about being an exception with my house.