C16 Century House Damp Issue

[Chinny]

Hi all,

Last year we purchased the below c1500’s semi-detached property.



We had a level 3 survey done and it didn’t flag immediate works but some works that needed doing in 3-5 years. The main two were firstly removing the cement render around the base of the building and replacing with lime. The second was to lay additional felt around the edges of the roof where it had deteriorated/fallen away and put new gutters in to improve drainage.

Over the winter I noticed that the plasterboard in the lounge was starting to warp and at one point we had mushrooms growing on the sole plate. I decided to cut some holes in the plasterboard to investigate and was a bit shocked/upset to find completely rotten timber the other side. In parts about 2/3 of the soleplate is gone. There was some form of fibreglass insulation with a foil backing that had soaked up the moisture and it was unable to escape. Since cutting the holes that area has dried out.


I’ve had a quote from a builder to remove the cement, re-render in lime, put in a french drain (as per survey guidance) and repair/replace any damaged sections of beams. To do the 12m section of wall, the quote was £30k and just recently for no reason they called to say it had gone up to £36k. I’ve since had a surveyor, who lives in the village, come over to take a look. He seems to think its not necessary to remove the cement as the wall cavity would dry out with central heating and more airflow between the cavity with a more breathable plasterboard.

Considering that area is bone dry now there then he is probably right. A cheaper and easier solution may be to remove all the plasterboard and the dodgy insulation and replace with a more breathable insulation and plasterboard, once the sole plate and beams have been repaired/replaced. I wondered if anyone else had something similar? I know taking the cement off the outside will be a massive job and potentially open up a can of worms.

My main questions are

1. Has anyone had any experience in this and any advice they can share?
2. Do people think it may be worth trying the cheaper option of still putting in a french drain but leaving the cement render and just tackling the issue from the inside?

Any comments are appreciated.

Thanks,
Alex

 

[jamest]

A couple of things occurred to me looking at your pictures and it may help others comment if some issues could be clarified.

Is the house listed? I assume it is, but if it isn't, your life is a bit simpler.
The 'sole plate' visible in the interior photos is clearly a relatively recent replacement. Is it rotting on the exterior side or is it a facing piece with part of the original on the outside? The posts don't appear to be tenoned into it as there are no peg holes - are they just resting on it?

Are the posts rotting on the exterior side? They look pretty good on the interior side for several centimetres, perhaps as much as 10 cm. For listed buildings, the general approach that gets approved is to preserve sound original timber, so those posts probably wouldn't be replaced, but facing pieces fixed to the exterior side where needed.

How are the frame infill panels actually constructed? From the pictures it looks as if there is thick cement on the outside (what's it fixed to? Some kind of mesh or a panel of some sort) with a drywall type construction on the interior side, i.e., battens and plasterboard - is that correct? Is your idea to remove the drywall and replace with some kind of breathable insulation? The problem there is that if the external face is a thin skin of concrete + whatever it's stuck to, water vapour will migrate through the insulation and condense on the external skin (interstitial condensation), which will create problems of its own as it won't be able to escape quickly enough. The exterior of the infills really needs to be 'breathable' as well - e.g., 25 mm wood wool board with lime render. A breathable exterior is the recommended approach when using cork or wood wool insulation. If you try to prevent moisture getting in or though using membranes, you will inevitably fail, it's virtually impossible to get these things air tight when retrofitting.

The ground levels appear to be below the floor level judging by the exterior photo. Is that the case? Ideally the ground needs to be well below the level of the bottom of the sole plate so that the plinth is exposed (it should be breathable, so if that black paint that appears to be on it at the moment isn't, it should be stripped off) once that's done, a French drain would only be needed if there's a drainage problem.

It's possible to 'bodge' these things and hope for the best - that's how it was done in the past! - but it's obviously better to do it properly. In such circumstances, it's definitely worth getting someone in who knows how to do it properly (e.g., a heritage timber framer) to assess the situation. It won't be cheap to repair/restore, but could perhaps be done little by little and the infill panels can be DIY'd - I've done a couple myself and it wasn't too difficult.

Anyway, that's what occurred to me looking at your photos . . maybe someone else on here can provide some more specific advice.

 

[Chinny]

Thanks for the response James. I'll address your comments in order.

The house is listed so I will need permission for the works we do.

The sole plate in the photos is not original and is rotten the other side of the plasterboard. The same for the post posts they're rotten externally up to varying lengths 20-30cm off the sole plate. They are just resting on the sole plate. I should take more plasterboard off to find out how high it goes exactly but havent yet been brave enough.

The construction seems to be batten and lathe (the bits I can see dont look original) then a metal mesh on top and the cement on top of that, this picture may show better. I assume the plasterboard is just fixed to the battens though not sure how.



The outside ground level, due to the tarmac driveway, is quite high and about the same height as the sole plate. This was the reasoning for making a french drain to lower the water level outside the house.

Even if moisture condenses on the inside of the external render, with sufficient airflow (like the current situation) then surely that would dry?

If the standard approach is to preserve the original timber and strap new timber on the external side I assume this cant be done unless you take the external render off?

My concern about lime is that is crumbles and doesnt last as long so I worry that I would just be trading one problem for another.

Ultimately if i just cut holes at the bottom of all the interor panels for now then that stops it getting any worse as the air can flow, the only downside is the place will just look like a building site.

We may have to bite the bullet and go for the proper repair its just cost being the issue especially as we should probably sort the roof first and the quote for that wasnt great either.

Thanks again.
Alex

 

[jamest]

I think I can see the infill panel construction now - it's a rockwool (or similar) insulated space with cement render applied to a mesh over lath on the outside and plasterboard on the inside. As you say, if air can circulate in the panels, then any moisture can get out. Problem is, what happens to the moisture higher up? What happens on the exterior faces of the posts (which seem to be rotting a bit at the base)? How will the air circulate in the panels if they are only open at the bottom? Unless they are open at the top as well, air won't really circulate much.

Cement render is a problem if there's moisture behind it. It can penetrate in from the outside through cracks (and since cement is hard and timber moves, cracks are inevitable) and it can condense on the inner surfaces: in the winter a few centimetres of exposed cement render is like a single glazed window, water will condense on it in surprisingly large amounts. If you do what you're suggesting, then the bottom will be able to dry out, but higher up there is ample opportunity for moisture damage. From what I can see, the posts are in pretty good nick, you may find that higher up the wall there is very little decay at all - that was the case in my last house, which was cement rendered with a diamond mesh over the timbers. If so, a good carpenter may be able to scarf facing pieces to the rotten ends of the posts at the bottom and the rest of the posts further up will be fine and you wouldn't need to remove much render. Could probably do something similar with the sole plate as what you've got there still looks good and thick. You'll never know what's happening further up, of course, without looking and it's typically the joints higher up the wall that rot, the faces not so much. From the looks of it, you might be lucky and find that significant damage only exists at the sole plate level and the base of the posts - fingers crossed.

I can assure you that lime doesn't crumble if it's properly applied. I've done a lot of plastering in lime both interior and exterior and it's not crumbly at all. Many historic buildings have lime in them that is many hundreds of years old and still good - that's not the case for portland cement, which was only invented in the 19th century. Portland cement sets very hard and is brittle - it's liable to crack and delaminate from old structures that move more than modern ones. Lime is softer and more forgiving (except for the harder hydraulic limes). Roman cement is a kind of hydraulic lime and was used to construct the dome of the Pantheon in Rome in 126 AD and it's still standing in almost perfect condition - it was the largest unreinforced concrete dome in the world for nearly 1500 years. Modern portland cement concrete structures often collapse after only a few decades! Lime also produces a much more moisture resistant interior surface than gypsum plasters which typically become soft and mushy when moist.

 

[Kearn]

My concern about lime is that is crumbles and doesnt last as long so I worry that I would just be trading one problem for another.

That statement unfortunately tells a lot. It couldn’t be further from the truth.

My current project, as with previous, have 500+ year old original lime happily still doing its job. It’s only when idiots come along and add modern inappropriate materials that issues occur.

Your builder really sounds like a jack of all trades. Not someone qualified to work on a listed timber frame property. His advice is incorrect and he shouldn’t be employed to damage the built heritage you’re currently a custodian of.

If your timber framed house is covered internally and externally in all the wrong materials as it appears, plus high ground levels, you can bet your granny’s pension, that you have many hidden issues, quite possibly serious and structural.

To put them right properly is expensive, timely, intrusive and very difficult as you need the right people with the right skills and experience, and they’re thin in the ground.

Your first quote is also not worth following through with, as there is no way that anybody can (or does) quote for heritage timber frame repairs as it is impossible to evaluate the scale of issue and repairs required until all four faces of the timber are visible to physically inspect. All conservation timber frames will work on a day rate or a range of quotes based on L/M/H scenarios.

 

[Chinny]

Thanks both.

The comment about lime crumbling was only based on some of the properties I've seen in our town. I assume then that they have been done badly.

Fortunately I do have a good builder booked in this summer who was recommended by the original surveyor and works only on heritage sites. His quote was more of a maximum expectation for the one wall.

The secondary advice was from a surveyor I met who lives in a similarly aged timber framed property in the village though I don't think he specializes in old properties.

The reason for this post was to gauge the opinion of people here on whether it's worth trying something cost effective and less upheaval for the building or whether it should be done by the book. The result of the beams drying out when the panel was open made me consider this. I think for my own piece of mind and because we plan to stay here for a good while I should get it done properly

It's quite worrying the prospect of having the posts rotten higher up, I assumed the moisture was just coming from the ground. I will have to open up some of the panels upstairs to check on them.