Ground beam repair/maintenance

[Mrs McG]

I’ve been clearing the front garden and discovered what looks like a ground beam under the soil and plants. Could this have been done to tackle settlement? The cottage certainly slopes!

Anyway, the section nearest the front wall seems to be covered by a tough fabric and bitumen paint, but as you can see the rest of it is concrete. A section of this looks like it’s fallen. I just wondered if this all looks about what you’d expect of a 1600s cottage or whether there are signs of problems that I ought to get checked out?

 

[Cubist]

Thatched houses tend to shed rainwater up to a couple of feet from the walls of the building but winds will often drive it back against the walls. If the lie of the land or the soil itself is not 'free draining' the water can collect near the sill beams of the timber frame and can induce rot. I've never come across the approach you have there before but the logic to keep rainwater away from the timbers is sensible. However, I would be suspicious of the efficacy of a bitumen coated fabric over the sill timbers as this could trap water behind it - both rain water that gets behind it and that that may collect from indoors. I would give serious consideration to getting rid of the bitumen/fabric coating and checking the condition of the sill beams.

There is another consideration regarding timber frames as the frame structure can be likened to a network of streams and rivers insofar that water penetration anywhere above will try to find its way back to ground. In this analogy the main posts of the structure operate as rivers and the beams are tributary streams, Most such water will head to the sill beams and this is one of the principle reasons why these timbers are more prone than others to wet rot.

 

[Cubist]

I'ver just noticed in your second photo that there may be a stone/slab-stone plinth under the sill beam? Is that correct and does the plinth slip away from the house and out into the garden?

 

[Mrs McG]

If a plinth is the concrete area that’s half painted / half not then yes, it slopes away from the cottage slightly. Perhaps I was using the wrong terminology calling it a ground beam?

 

[Kearn]

That concrete is neither a plinth or a beam! And no, it certainly should t be there.

Hard to tell where your (wooden) cill beam is in the photos, or if it still exists. The smooth black painted vertical is presumably a cement render, either over the beam or timber the bricks / other, which have replaced it historically when it failed. Either way, it’s not a great material and will trap moisture behind resulting in mould / rot etc. it should be removed and the wall assessed, dried out and replastered in lime if required.

The concrete on the ground will be holding ground moisture against the building, and also won’t help with splash back against the building, neither are things you want. It ‘may’ have been added as a crude attempt to shore up the plinth under the cill beam, but I imagine if you dig down against its edge, you’ll find it isn’t too deep and is effectively a surface coating. Which should be removed ideally, ensuring external ground levels are at least 6 inches below internal. And then a French drain or similar considered for moving moisture away from the building, if it isn’t possible to ensure the ground level away from the building is at that low level completely.

However, these are the correct approaches, but you haven’t mentioned any context or issues - what are internal vs exterior ground levels, what’s the internal floor construction, what is the wall construction and internal / external coverings, have you got damp/mould/bubbling paint/effervescence ….

You don’t need to go looking for work! But if it was me, I’d get rid of the concrete surface and ensure external levels are lower than internal and see whether I still had a cill beam and what condition it was in, then make an informed decision

 

[Cubist]

If a plinth is the concrete area that’s half painted / half not then yes, it slopes away from the cottage slightly. Perhaps I was using the wrong terminology calling it a ground beam?

No. If there is a plinth it would most likely be constructed of stone or perhaps brick. The timber cill (forgive my earlier misspelling - autocorrect, what can I say) would have been mounted on it as an established level for the frame of the house. My assumption was, and remains, that the cill timber is directly behind the vertical section of bitumen painted material. If it's the fabric you referred to then it needs to come off. If it is in fact a mortar render then more care may be needed unless you intend removing all of it.

If the concrete is very shallow and has been shaped to cause rain-water shed by the roof to splash away from the wall then its doing no harm and is own fact helping as the rest of the garden seems to slope away from the house. But, if it's more than a few inches deep and/or deeper than the top soil it will indeed be trapping water against the house, in which case it needs to go.

Should you choose to remove the concrete be aware that PO's may have used it to 'stabilise' the exposed face of a stone and rubble plinth and you should exercise caution with those sections within 6-8 inches of the external wall.

 

[Mrs McG]

Thank you both, I understand the gist of what you’re saying although not all of the detail and it sounds as though I ought to get someone like a structural engineer with relevant experience to take a look, is that a sensible next step?

I emailed a photo to the surveyor I used to purchase the cottage and their view was that it was likely an old ground beam / wall plate and I just needed to keep it maintained. They are specialists in listed buildings so I’m a bit horrified to see how different their view is compared to the ones here!

 

[Kearn]

Thank you both, I understand the gist of what you’re saying although not all of the detail and it sounds as though I ought to get someone like a structural engineer with relevant experience to take a look, is that a sensible next step?

I emailed a photo to the surveyor I used to purchase the cottage and their view was that it was likely an old ground beam / wall plate and I just needed to keep it maintained. They are specialists in listed buildings so I’m a bit horrified to see how different their view is compared to the ones here!

Sadly your surveyor sounds like they are creative, and probably not versed in timber framing, which not many are - I have no idea what a ‘ground beam’ is meant to be… I assume cill beam / sole plate (interchangeable terms) but that is the perimeter of your lowest rectangle of your timber cuboid building. It can be close to ground level, set only on pad stones as foundations, but often higher on a raised plinth to keep it away from ground moisture. It would never be underground! It also wouldn’t step outwards like that, if it was wider in section that the vertical posts of the frame, the extension would be internal, not an external rain trap.
It could never be a wall plate, unless someone has tipped your house upside down…



How are your internal floor levels compared to outside? It could be that the garden has been raised significantly, it happens.

 

[Cubist]

Yes, it's far too easy for confusion to creep in and sadly sometimes it's not just the words we use; oftentimes the photographs and illustrations we use can be the cause. Setting all that aside any thoughts of engaging a surveyor right now are very premature as I believe there is a vary simple explanation for the stretch of concrete outside your house and the previous owners use of bitumen coated fabric.

As stated in my first reply, rainwater run-off from a thatched roof can fall up to a couple of feet from the face of the walls. During heavy rain-fall that run-off can verge on the spectacular and seem to descend in sheets and torrents. If it were to fall directly onto a soil surface it would, as it does here at my home, quickly excavate a channel up to a couple of inches deep in the soil. While doing so muddy water would splash back upward and, again as it does at here, some would cause the accumulation of muddy stains on the walls of the house. I believe that a previous owner of your house decided to lay that bed of concrete to prevent such regular occurrences and save him/her the regular job of cleaning the resulting mess off the surface of what may be a very coarse render.

However, that previous owner may also have gone a step too far by installing the bitumen coated fabric nearer to the wall of the house and perhaps up over the face of the timber cill/sill beam. Whilst the rationale of stopping staining of the walls may work very well it does introduce a threat to the sill timbers as described earlier in this discussion.

To reiterate; the concrete pad, provided it is not thicker than 2-3 inches, can do no harm. But, if it is deeper than the top soil it should be removed. The bitumen coated fabric needs to be removed as this could contribute to wet rot in the cill/sill timbers.

When you have exposed the sill timbers post a photo here if there appears to be any significant damage to the exposed face. Only then might it be worth consulting a specialist surveyor.

Hope this helps, cheers,

Cubist

 

[Mrs McG]

Thank you both so much! For context, the ground level at the front is definitely not 6 inches below internal level but I will look more closely at this over the weekend. I suspect the concrete is only a couple of inches deep so your explanation Cubist makes complete sense, but I will investigate that too and post back here when I know.

 

[Mrs McG]

I had another look this morning. The ground slopes very slightly away from the front wall of the cottage, I’d estimate 2 or 3 inches across an 8ft depth of front garden. If I lowered the soil level to create a greater slope away from the cottage then where my boundary meets the road my garden soil would be several inches lower.

As for the concrete ‘pad’ this indeed looks to be about 3 or 4 inches deep. The photo below shows a gardening hand fork which I got underneath the concrete. The concrete slightly slopes away from the cottage and where it meets the soil these levels are the same. The soil had run almost up to the wall and there were several shrubs planted right up against the concrete but I dug them out and cleared all soil from the concrete.

The fabric with bitumen paint seems to have been used to carry away any water that falls down the front of the cottage. It curves from the concrete pad to a couple of inches up the front wall render. The render is cement so I would think that a couple of inches of bitumen on top of that isn’t doing any extra harm? There are no signs of damp internally.

A few photos below which may help where my words haven’t. Any thoughts on whether to leave well enough alone until I have enough cash to replace the cement render? (if ever or unless forced to, let’s be honest).

 

[Cubist]

Sounds like rainfall, or that shed from the roof, driven against the wall was puddling at the foot of the wall and above the edge of the concrete pad. You've done the right thing by clearing away the shrubbery as that will assist the drainage of water thus trapped to find a way out under the concrete. A French Drain would be a better solution but that would mean digging out the concrete pad.

As you seem not to have found a timber cill beam near the foot of the wall it's probably safe to assume that the render may have been applied over it, if indeed there is one. Frankly I would leave it alone now until you're ready to deal with the render. One thought though, you may be able to confirm whether there is a cill beam behind the render by checking indoors at the foot of any visible vertical posts.