An introduction... Renovation + 1950s + subsidence = a challenge!

[alfaTom]

Hi everyone! 

Thought time to make myself known as I will inevitably be asking some questions shortly.

At the start of the year my wife and I found a project house that had the potential to be the 'forever home'. We got the keys last week so we're finally getting started, and whilst she has it all on Instagram I doubt I'm going to get any decent discussions going in the comments on there compared to here.

Now, onto the house... it's a 3-bed detached house on half an acre of land, estimated to have been built around 1950s. It's had a couple of extensions during it's life although we are likely to take them off and start again. Heating is an oil boiler, drainage/waste is via a septic tank, windows are old aluminium DG units and the garage is waiting for a decent wind to fall over. The house does have BT FTTP though so it balances out pretty well all things considered...

 

 

Did you say subsidence?!
Yep. Built on clay soil in Lincolnshire when the house was first built they planted trees. A LOT of trees. I don't think it surprised anyone when they all matured and absorbed all the moisture in the ground. In 2012 the house suffered subsidence with cracking in the walls. This was repaired with helifix tie bars and the nearest trees being removed, but no underpinning. A CSA was issued confirming all was well. Fast forward to now, and there are some decent-sized cracks in internal walls which suggest new movement.
Structural engineers have been and gone, and they've said the outside of the house looks good with few cracks and no split bricks, the roof trusses are in good condition (free from stress) but they'd have to assume there has been further movement due to the internal cracking. We purchased the house from the previous owner's daughter so we have little historical information to go on aside from what we can find out.

 

What next?

We're in this for the long haul, and we're living in the place while we do it up. I know, I know; we're mad but we have no other commitments or responsibilities so now is the time to do it. It's old, it's leaky and it's in need of some TLC.
Architect plans are being drawn up, subsidence underpinning companies have been drafted in and hopefully, in a few weeks, we'll have a date for getting that resolved.

The plan is to seal up the house as best we can, then go for ASHP/Solar/UFH/MVHR to get as eco-friendly as possible. Current EPC is an F, as in "F**k, that's a bad score"
I'll leave that for another post however in case your attention span is as good as mine...

[Mr Punter]

Demolish and rebuild may be best.

[alfaTom]

It had crossed our mind, but we're confident the source of the issue was soil desiccation from trees and can be managed.
We'd rather keep the house as it has some history instead of knocking it down.

Once underpinning is complete we'll be fully covered by our insurance provider so whilst any future movement would be a pain it wouldn't have the same financial impact to resolve.

Appreciate the callout though, always good to challenge things to see if a better alternative out there.

[twice round the block]

subsidence. 

I know the feeling 

[Mike]

 

5 hours ago, alfaTom said:

Once underpinning is complete we'll be fully covered by our insurance provider

That's a start but I would expect (though only from the very many press stories on the topic over the years, not personal experience) that it will be for a substantial premium. You may also find it difficult to move to another insurer in the future, leaving you unable to avoid whatever future premium increases are demanded of you. Not to mention the added difficulty of eventually selling it; once a house has been underpinned it's going to be labelled that way for decades into the future, whether or not there has been any movement. And any further settlement after underpinning, while it shouldn't happen, would only add to these issues.

 

 

6 hours ago, Mr Punter said:

Demolish and rebuild may be best.

 

Unfortunately I completely agree. Underpinning can almost certainly solve the problem technically, but not financially.

 

Rebuild and take advantage of the opportunity to achieve - ideally exceed - current insulation requirements, and the 0% new-build tax rate.

 

Edited July 5, 2023 by Mike

[Kelvin]

Rebuild and start again very much dictated by purchase price I’d have thought 

[alfaTom]

Morning all, few replies to catch up on!

 

Thankfully our subsidence is nothing like that @twice round the block otherwise we wouldn't have bought!

 

Whilst I get the calls for rebuild and agree it would result in a better and more modern home it's not on the cards. The house is 200 sqm and our budget is not likely to cover a rebuild of this scale to our desires.

 

I work in the insurance industry so thankfully know a bit about the perils and how to go about insurance for a property like this. Unlike what the media proclaim we've been able to obtain reasonably priced policy with good coverage (£550).

 

Our intention is to live here for a long time so the resale value isn't a primary concern, but we're happy that we bought for a discount so will have to sell for a discount.

Either way the intention here is to be open & honest and document our findings for others to benefit from.

 

Back to the property however:

Prepped to lift floorboards yesterday but the dishwasher developed a drain fault so I didn't get to see what was under there. A job for today perhaps...

[Dave Jones]

lot of cash can be saved on VAT if demolish. all depends on level of work you planning / costs as allways!

[ProDave]

What nobody has talked about is "half an acre of land"  Is there the potential to repair the current house and live in it, then build a new one in half the garden?  Eventually selling the first house.

[joe90]

Welcome to the Buildhub. I too would consider a demolish and rebuild but if you have made that decision so be it. Is it cavity wall? What size? What insulation will you need to meet regs?, these are all things that renovation is harder than re build!. I would cost both routes first with the advantage of better re sale price in the end. Bring on the questions. 

[alfaTom]

thanks all, as mentioned before a rebuild would be nice but realistically it's not going to happen - whilst we have a decent amount of funds to use it wouldn't cover a rebuild, whereas a renovation allows us to start different stages as and when funds allow.

To answer @joe90 the main house is constructed with cavity wall, external walls being about 250mm thick. CWI already in place and some old 80's glass fibre insulation in the loft. Appreciate it will be harder to get to some of the targets on energy efficiency but there will be some easier bits to tick off such as replacing the old windows & doors, improving loft insulation etc. 

The plan is for some form of cladding or rendering externally in the future which could be linked with EWI if needed to hit the right U-values.  

[twice round the block]

Hope the wall ties in the cavity haven't started corroding, as you'll be in for more than piling and under pining to guarantee the structural integrity of the building.

Have you made enquiries from a kit house company to see what the cost would be?

 

There's a lot of experienced builders on here that have worn the T shirt, hence why the advice to demo the original and do a new build. 

The cost's on renovating will spiral.

[George]

Lets see these cracks.

 

Cracks on old buildings is not unusual - it could well take a decade to settle down completely but crack stitching + underpinning might just mean more cracking. I try and reserve underpinning for actual subsidence (loss of soil support due to washout etc) or undermining/basement work. Tackling ground movement with underpinning is a sledgehammer to crack a nut. 

 

I'd certainly undertake the following prior to doing anything drastic:

- trial pits to determine actual foundation arrangement

- a programme of crack monitoring for at least 6 months, ideally 12, to determine whether it is seasonal movement or not

- ground investigation to get accurate information on soil type, plasticity and water level

 

Underpinning is a substantial upheaval to a building, let alone cost, and a few thousand on investigation work is well worth it. Slightly surprised the structural engineers didn't suggest this.   

 

Edit - good suggestion regarding wall ties. This would normally effect the outer leaf but it would not be unknown for inner leaf corrosion to be noticed first, especially if the outer leaf had been repointed in (relatively) recent history.

Edited July 10, 2023 by George

[Mike]

On 10/07/2023 at 23:19, George said:

Underpinning is a substantial upheaval to a building, let alone cost, and a few thousand on investigation work is well worth it.

Agreed; the underpinning needs to be designed to suit the specific building and circumstances.

 

On 10/07/2023 at 23:19, George said:

Slightly surprised the structural engineers didn't suggest this.   

Presumably just a pre-purchase visual inspection?

[alfaTom]

On 10/07/2023 at 23:19, George said:

Lets see these cracks.

 

Ok - as requested pictures below. Internal cracking looks to be worse than external. I've yet to have wallpaper/plaster off to check behind as had been waiting for a specialist to see it before I hack the plaster away.

 

 

Above is cracking on the doorway between old house and the extension. Below is the external join.

 

This one is towards the bottom of the property in the front left corner of the property where there seems to be the most drop. It's also next to a gutter downpipe where the soakaway has failed.

 

There are other cracks throughout the house that generally suggest the house has sunk along the front aspect. As mentioned previously the structural engineer said he did not feel the roof was being stressed too much and the only reason he'd say it was suffering from ongoing movement was due to the fact the internal cracks had not been covered.

We've had TPs and SIs done as well as drainage surveys and I had the info through today, although I am not yet fully understanding of the info. The soil lab results for TP1 (which was completed close to the extension join) is below:

 

There is other data for me to go through, or if people wish for me to upload it I can look to do so, but didn't want to dump it all on you.

 

@Mike the initial structural engineer visit was just a GSI for the whole property, although this was from a proper MIStructE fella.

 

I had to clear out the drains yesterday as they had become blocked from debris, that plus some misaligned drain pipes and the failed soakaways would suggest some soil washout in addition to the previous desiccation via nearby trees. 
As you'll note from the first image I've started a basic monitoring across some of the cracks, although I do not believe they have gotten worse over the past 6 months. I wouldn't be too concerned about external cracks along mortar lines as we have had some very hot weather to allow for some seasonal changes, but I am less keen on the cracked brickwork and the internal cracks.

The ground slab has also dropped and sloped towards the corner referenced from picture 3, but I've not investigated it yet to know the composition below.
I will have to look into some cavity wall tie investigation work as that is a good shout. I know the house was originally built by the owner, and the construction itself does seem to be pretty good (some good detailing around the joist pockets on internal walls and not loads of crud left under floors etc), but I guess they didn't foresee the tree/ground issues.

[twice round the block]

The cracks above the doorway don't look that bad. Hack off the plaster and see what lintel is over the opening.

 

Cut out a couple of bricks where the extension meets the original build and see if it's tied in properly. I would say it's tied in with some frame fixings or similar to the original part of the house.

 

Lift up the carpets at the front of the property if that's where you think it has dropped and see if there is a gap between the bottom of the skirting and the floorboards.

Do a ball test on it and see if the ball rolls down hill, towards the skirting. 

Samples from the bore holes don't look too bad, little bit of sand and gravel but not excessive. 

 

When the property was built by it's owner the building regulations we're poles apart from where they are now. so tieing in the extension with galvanised frame fixings every 6 course's, and thin prestressed concrete lintels over doorways we're passable then especially with lax planning departments.

Edited July 13, 2023 by twice round the block

[alfaTom]

Will make that a weekend job to do a bit of discovery, cheers for the suggestion.

It's definitely dropped as there is a significant slope. A lot of the floors in the house are uneven, but the plan was always to have them up and insulate + UFH so as long as the underlying (no pun intended) problem is resolved we should be ok.
A few more pictures of other sections:

This is above the doorway crack, as you can see the plaster side has cracked a bit more dramatically than the side without plaster. You can also see where some remedial work has been done in the past.

 

This is the upstairs landing where it has cracked from the doorway in the front bedroom (right image). This crack runs along the ceiling to the bathroom door, but as can be seen in the left image there is no cracking visible from this side:

 

Finally; the downstairs dining room floor. Whilst the floor meets the skirting still, there is a fair decline to the corner. This is the corner referenced in the outside picture of my previous post. I'll be moving the large rose bush at the weekend from it and clearing the rest of the vegetation around it to see what state the ground/drainage is in. I may also try to cut out a section of the ground slab to see what the construction is like beneath it.

 

We always expected to redo the interior walls/floors/ceilings, but we just want to make sure the movement isn't ongoing before we start work.
 

 

[twice round the block]

Because your house was a self build by the previous owner, you don't know what his skill set was, or if he had any.

 

Looks like the ceiling boards didn't have scrim joints to open like that. 

Yet another crack above a doorway with an unknown type of lintel. 

 

Did you ever get a price from a kit house company so you know where you're maximum renovation budget should be?

Gutting this house and renovating it could cost nearly as much as a well insulated, modern new build. 

 

Fact. it is faster to demolish a property and build new than it is to renovate an existing one.

[Iceverge]

@alfaTom

 

Welcome Welcome Welcome. 

 

Looks like a nice spot from the top pic. 

 

On 06/07/2023 at 07:08, alfaTom said:

I work in the insurance industry so thankfully know a bit about the perils and how to go about insurance for a property like this. Unlike what the media proclaim we've been able to obtain reasonably priced policy with good coverage (£550).

 

Excellent News. 

 

Have you considered burning it down? 

 

[Gus Potter]

2 hours ago, alfaTom said:

Will make that a weekend job to do a bit of discovery, cheers for the suggestion.

Yes do that before you embark / commit to anything. You could potentially save thousands here.. pick the wrong solution and you could lose thousands more!

 

5 hours ago, alfaTom said:

We've had TPs and SIs done as well as drainage surveys and I had the info through today,

 

My immediate thought is this.. well I'll start with a bit of background info to explain... and Linconshire is a great example.

 

For all. Often you may think that deeper founds = more soil bearing capacity = more load you can put onto the ground.

 

But in parts of the UK we have "upside down ground" yes deep down there is rock / good sand / gravel etc but this can be far down.. Here the ground nearer the surface has a stiffer crust and below there is softer material that doesn't  behave well. In other words digging deeper causes more problems than it solves. A lot of houses in Linconshire / small industrial buildings too have deliberately shallow foundations that sit in the stiff crust near the surface. The load is then spread out so by the time it reaches the softer layers the stresses are reduced on the weaker layers. The reduced stress causes the lower layers (weaker soil) to compress less and this reduces the settlement.

 

@alfaTom If you look at your results you can see that the shear vane value reduces a huge amount with depth. We use the shear vane value as part of the calcultation to determine the bearing capacity of the soil. Also you can see that the soil classification changes with depth. At all levels you have what is called a plastic soil.. more prone to settlement. But the deeper you go the more plastic the soil becomes.. in other words worse.

 

The trial pit result shows that the soil changes to something possibly more favourable at 3.4m depth as it is starting to transition to a sandy layer which is more ameniable.. but you may need to go a good bit deeper to get to something sound.

 

There are loads of houses in Linconshire and elsewhere that are built on the stiff crust. The house does go up and down a bit but the secret is that it all moves up and down at the same rate and that is why many of the houses have not fallen apart.

 

You have two different types of loading on the soil.. from the single story part and a two story part. Both load the soil differently so will move by different amounts, hence the cracks you see.  Do you know what came first?

 

This underpinning stuff.. what are the companies proposing? and how much?

 

I think more time needs to be spent understanding how this old building works and the ground under. Then you design for the movement when you want to make changes, save a load of cash. You SE has said that the cracks are not a big problem so the building as it stands is not structurally unsafe.

 

If it was my house I would be asking the underpinning folk.. are you sure that you are not going to make things worse and can you prove it!

 

Looking ahead you may want to extend and go for high insulation and energy efficiency.. say Passive design concept. Here what we do is excavate out the soil, stick in loads of EPS and deduct the difference in soil mass.  we play about with and take advantage of the light insulation and balance that with the loads the old house is putting on the ground so we can make a good attempt at making the old bit and new bit move up and down in the same way and that reduces differential settlement. Just if we do this we need to make sure the new bit does not float as EPS is lighter than water.. we need to look at water table and flood risk.

 

Once you get your head round the fact that your building moves up and down you then design your investigation strategy around this. You gather the facts and prove it SE wise.. they did it for the Pizza tower.. we can do the same in Linconshire. for less cost! Crack stitching in this case on this type of soil often just results in moving the problem somewhere else. Often we want the building to be flexible.. like using lime mortar.. so we get lots of little cracks rather than a few big ones.

 

Keep us posted.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Gus Potter]

On 05/07/2023 at 17:25, alfaTom said:

Thought time to make myself known as I will inevitably be asking some questions shortly.

Double post here alfaTom... as I'm on a roll.

 

Last post was about the ground but once you know how you building works what next.. how do you design to take account of the movement?

 

To start.. what do you want to do internally.

 

First I look at where the movement takes place. If we wanted to change some non load bearing walls inside then look at doing them in light weight frames, could be timber or metal stud for example. But these panels are quite stiff, but not heavy. You have a square and stiff panel  attached to an old building that is moving up and down, probably differently at the edges of the panel. An easy way of dealing with this is to introduce shaddow gaps around the edges of the stiff panels so the movement cracks are hidden. The beauty of this is that it allows a huge amount of flexibility in the interior design.. and future proofing. You can change each panel without having to redecorate the whole room.

 

Floor coverings.. well go for flexible floors that can take a bit of distortion.. say 25mm! That leads you down the timber / carpet /Lino tile type route. You could have small areas of ceramic tiling.. but that will come at a cost.

 

Externally you can use drain pipes to hide joints, sometimes plants..  a treliss..

 

If you want to make structural alterations inside, say knocking a hole in a wall then you end up with point loads on the founds / underbuilding. To get around this you can use a box frame that "tricks"  the found into thinking that nothing has changed above.

 

Going back to you original post I would explore every avenue before commiting to underpinning.

 

 

 

 

 

 

 

[Mike]

5 hours ago, alfaTom said:

A lot of the floors in the house are uneven, but the plan was always to have them up and insulate + UFH

Underpinning methods vary, but it's very likely that the floor along at least one side of the internal walls, and quite possibly the perimeter of all the ground floors, would have to be broken out anyway in order to undertake the underpinning, so it's a good idea to replace them entirely.

 

You also need to be sure that the new floors aren't going to move; movement in a floor with UFCH pipes embedded in it could eventually be very problematic.

[markc]

You also need to be sure that the new floors aren't going to move; movement in a floor with UFCH pipes embedded in it could eventually be very problematic.
 

this is a very good point and one overlooked too often with renovations and building changes.

a guy who works for us recently asked me to take a look at his parents new conservatory that is sinking away from the bungalow. It’s not! The conservatory builder has seen the poor ground and slope so dug very deep footings onto solid ground but the 50’s bungalow is sitting on top of the clay and moves with it, so it’s the bungalow moving and the conservatory staying still.

[alfaTom]

Lots to unpack here from yesterday and today's replies...
First off thanks to all that have responded, it's appreciated and the wealth of knowledge here is astounding.

So the previous owner who built it was a builder by trade and he's built a few houses in the village. I know he built the bungalow next door and that has been underpinned with no further movement apparently but no details on the rest.

 

@Gus Potter wow - those are some detailed responses there! To answer your questions:

The 2-storey part of the house came first. The 1.5-storey extension came after, believed to be completed late 1970's just before the chap passed away.
The underpinning company we have been talking to is Geobear, who do a resin-injection form of underpinning rather than traditional mass concrete. This was after the SE said that the resin injection may help to stabilise the house & lift the ground slab.

Below is their suggested works, which involve resin injection across the majority of the front elevation as well as around the gable ends. Total cost works out about £30k inc VAT

 

I honestly did not know about the "upside down" ground aspect and this is something I definitely need to look into more, especially as we'd rather use that cash on other parts of the property if the underpinning is going to cause issues with the rest of the property.

The use of shadow gaps and hiding expansion points is a great idea, and one I had already been thinking about when it comes to replacing the front porch.

 

There will be some non-load-bearing walls going as well as some load-bearing walls. We are looking to extend the utility bit into the Store/hall area as shown on the above map and extend out to the west from the dining room (this is a gable end so hopefully not as much load on it) Plans should be back from the architect soon at which point we will be able to have some informed discussions with SE on the best approach for what we are looking to do. There is a chance the foundations for the Kitchen and boot room extensions are not deep enough for a 2-storey build so they'd both have to go which would give us a chance to tie it into the rest of the property in a more sympathetic manner to work with the movement.

 

51 minutes ago, markc said:

a guy who works for us recently asked me to take a look at his parents new conservatory that is sinking away from the bungalow. It’s not! The conservatory builder has seen the poor ground and slope so dug very deep footings onto solid ground but the 50’s bungalow is sitting on top of the clay and moves with it, so it’s the bungalow moving and the conservatory staying still.

 

These stories plus Gus' explanation of the movement are definitely making me think twice about the footings/underpinning aspect. I had thought solid = better but I can see now that perhaps we need a better solution.
Whilst the SE originally surmised the ground had dried out to cause the subsidence initially I am not sure if the soil survey backs that. Perhaps some light reading tonight once finished with work!

Are there SE's that would specialise in this sort of soil or should all chartered Se's be good for working out the correct loading and understanding of the soil?

p.s. Happy Friday!

[George]

Quote

Whilst the SE originally surmised the ground had dried out to cause the subsidence initially I am not sure if the soil survey backs that. Perhaps some light reading tonight once finished with work!

When they say 'dried out' they don't mean literally dry. The water uptake from the tree roots will have reduced the moisture % in the clay soils causing volume change. The soil report doesn't appear to test for plasticity but they are clays and silty clays. Given the area of the country, medium to high plasticity is likely (medium to high volume change).

 

However... from the photos of those cracks, I think underpinning / soil injection will not be high on the list of options.

 

My plan would be

- repair drains! Washed out soil will need to be backfilled

- trial pits to inspect foundations around the building - to determine the various depths and width of the different parts. Say, one on each elevation - at the join of old & new

- monitoring of the cracks externally & internally using crack monitor gauges

- hack plaster off and have a look at the internal cracks properly

- consider movement joints if there is a step in the building superstructure and or foundation

 

You may still get fine cracking for the lifetime of the building but if I could do all the above for £10k, bank the £20k and just reapply caulk and paint every 5 years I'd be happy.