Questionable foundations...

[MattNor10]

Hi all, my first post as fairly new to the forum.

We bought a 17th Century timber frame house in Jan last year with the plan to do some light renovation that has escalated slightly.

Most issues seem to have been caused cement, either bad repairs or poorly laid floors with no real damp proof membrane. We have a fair few frame repairs to do and have a lot of damp pushed in to the walls (rotten sole plates and some posts, damp bricks on walls under cement render on Victorian extension, and the list goes on, none of which picked up by surveyor).

Enough of the rant

We are removing all the poorly laid concrete floors, letting footings dry out and replacing with limecrete (with foam glass).

On doing so we've uncovered some questionable footings under a chimney, see attached pics. I am obviously worried about disturbing something that's been there for hundreds of years but my builder is telling me we need to remove the boulders and rebuild footing, going deeper to more solid ground as they are effectively sitting on mud.

Generally the builder has been really impressed with the footings, they are couple of feet deep and he said that's unusual for this type of building. See attached pics.

Just wondering if anyone had a similar experience or has any advice?

Thanks in advance
Matt

 

[Kearn]

Footings a few hundred years ago are often very dubious by todays standards, yet the structures are still standing… with many timber frames, there often wouldn’t be much more than a few large stones a foot deep or so. Maybe a bit more for a stack.

I can’t see why the need to meddle and I certainly wouldn’t like to try underpinning an entire stack in situ unless it is actively sinking/leaning or there is an issue to resolve. Otherwise, chances are you will create an issue.

What would concern me with your pics, is how the sub floor has been excavated - with an old property the rule of thumb is to dig carefully at a 45 deg angle so as not to disturb shallow foundations. Going straight down against the wall to uncover them is far more likely to result in potential issues.

 

[Feltwell]

Agreed - if there's no sign of distress, leave it alone. If it's been sat there for many years and not gone anywhere, why should it start now? Most movement happens in the first few years of a building's life, unless there is something else at play such as a broken drain.

 

[MatthewC]

Footings ... We found that under a couple of buttresses on the church, there was just earth! I don't know how anyone expected a buttress to do its job without foundation, but it's been there since C14, so why worry now? The critical question always is whether there is any sign of movement and, if so, is it recent? If movement isn't recent then my personal recommendation is to leave it alone (and I am sure the church architect would agree with that).

I agree with Kearn that you should not dig vertically beside the foundations apart from the odd exploration. To reveal footings extending for yards is asking for trouble. I learned from a soil engineer that in a railway embankment the forces spread out at about a 15 degree angle from the vertical, so 30 degrees should be fine - I used 45 degrees when doing my limecrete floor. I had the same sort of worry as you with a chimney - we laid the limecrete floor around it pretty quickly and it's not been a problem in 11 years!

If you are worried, you need the advice of a specialist - our church architect is RIBA and AABC (Architect Accredited in Building Conservation) so she knows her stuff, whereas many architects and surveyors are not actually very knowledgeable about old buildings.

Good luck - keep us informed

Matthew

 

[MattNor10]

Thanks all, that's kind of in line with what I was thinking.

Appreciate advice, will discuss this with builder.

Will keep you posted

 

[Roger440]

Ive just done this. Recent post elsewhere on forum.

Unless theres evidence of movement, leave well alone.

 

[Gothichome]

I have to agree with the others, it has held up for centuries, no need to fuss with some thing that is working.
Ron

 

[worms]

Are you sure that footing is holding up the chimney, rather than just the fireplace? In the first pic, there is a beam at 90 degrees to the fireplace - is it structural? If so, does it rests on another across the top of the fireplace, with the actual chimney behind this? Are you able to do a tentative inspection dig at the outside behind the chimney to see what is going on below ground across the back of the chimney?

As others have said, if it ain't broke...!

 

[Gothichome]

Are you sure that footing is holding up the chimney, rather than just the fireplace? In the first pic, there is a beam at 90 degrees to the fireplace - is it structural? If so, does it rests on another across the top of the fireplace, with the actual chimney behind this? Are you able to do a tentative inspection dig at the outside behind the chimney to see what is going on below ground across the back of the chimney?

As others have said, if it ain't broke...!

Worms, are you thinking the fireplace is an infill inside another larger fireplace? My first thoughts were that those look like Victorian bricks. I would think a 17th century home would have had a large cooking fireplace complete with a swing crane and associated iron works. The two horizontal lintles look to be stone.
Ron

 

[worms]

Worms, are you thinking the fireplace is an infill inside another larger fireplace? My first thoughts were that those look like Victorian bricks. I would think a 17th century home would have had a large cooking fireplace complete with a swing crane and associated iron works. The two horizontal lintles look to be stone.
Ron

Ron, not necessarily an infill. It's perhaps just difficult to make out the configuration from the picture.

The picture perhaps gives a false impression of depth, but it looks almost as if there could be a core directly below the chimney stack and then a brick fireplace and hearth (with the dubious footings) in front of this. This would mean that the footings are not really needing to support much at all and are much less structural. The juxtaposition with that beam makes me wonder about the layout of the chimney in relation to the frame of the house

I guess I'm mainly wondering what is holding up the weight of the chimney stack. Your builder is questioning whether the visible footings are up to that job, but to my eye (and I certainly ain't no expert!) I would think you might reasonably ask the same question about the two sides of the fireplace. So my hypothesis is that perhaps neither of these elements is actually responsible for supporting the weight of the chimney stack. If that is correct, then the question is perhaps not about the visible footings at the front, but those that have not yet been exposed along the back wall of the fireplace.

But something is holding it all up and has done a good job of that for at least a couple of hundred years!

 

[CliffordPope]

Footings ... We found that under a couple of buttresses on the church, there was just earth! I don't know how anyone expected a buttress to do its job without foundation, but it's been there since C14, so why worry now?

Surely it's the weight of the buttress that holds the wall up, by leaning in at an angle? If the buttress had pefect foundations then it wouldn't sink at all so wouldn't be doing any buttressing?

 

[stuart45]

A buttress wall is better with a foundation as the force from a leaning wall is transferred to the ground through the buttress. When built it will tend to settle towards the wall.

 

[88v8]

We bought a 17th Century timber frame house in Jan last year with the plan to do some light renovation that has escalated slightly.

Most issues seem to have been caused cement, either bad repairs or poorly laid floors with no real damp proof membrane.
We are removing all the poorly laid concrete floors, letting footings dry out and replacing with limecrete (with foam glass).

The footing have been covered by other posters, with whom I agree.
Unless you plan to discover what is behind that (relatively) modern fireplace, get the floor filled in pronto. Our C17 has similar non-foundations under the walls, but we only left them unsupported for one day.

Damp proof membrane..... you should never put a dpm in a floor unless there is a working dpc in the walls. Otherwise, you will just make the walls damp.
So your limecrete floor should have no dpc, which I presume is the case.

Escalated... haha, join the club....

Ivor

 

[MatthewC]

Footings ... We found that under a couple of buttresses on the church, there was just earth! I don't know how anyone expected a buttress to do its job without foundation, but it's been there since C14, so why worry now?

Surely it's the weight of the buttress that holds the wall up, by leaning in at an angle? If the buttress had pefect foundations then it wouldn't sink at all so wouldn't be doing any buttressing?

If it has a foundation then yes, some of its weight will act against the wall. If it has no foundation then its weight is mainly acting against the earth. And in any case the buttresses I am talking about a very nearly vertical.