Is underpinning allowed under Class Q?

[ChrisF8]

We need some advice with a piece of land we’re looking to purchase. It has a single storey barn on it with class q approval. On further inspection the barn is sitting on a 200mm concrete slab that I’m presuming wouldn’t pass building regs as suitable foundations…so we would need to underpin it.
 

my question is… is underpinning classified as ‘new foundations’ or it reinforcement of the existing slab? Either way does this invalidate the granted permission as the class q conditions state:

 

• The regulations do not allow the introduction of new foundations, loadbearing floor slabs or significant rebuilding works.

 

[Jilly]

Welcome! It's a very steep learning curve. Take a look at the Little Stud Barn Blog, they are doing class Q. i don't think there are many on here who haven't got full planning permission (in the end, that is)

 

[IanR]

1 hour ago, ChrisF8 said:

We need some advice with a piece of land we’re looking to purchase. It has a single storey barn on it with class q approval. On further inspection the barn is sitting on a 200mm concrete slab that I’m presuming wouldn’t pass building regs as suitable foundations…so we would need to underpin it

 

Is it a reinforced slab. At 200mm thick it may well be able to take a timber frame construction on it. Building Control will be happy if the Structural Engineer signs it off.

 

But to your question... Replacing or reinforcing existing foundations remains a controversial area for Class Q (to coin Martin Goodall's phrase). Some LPA's are happy to Approve a Class Q conversion that will replace walls, floors and roofs putting additional loads into the existing structure, without any evidence that the existing foundations are strong enough to support the conversion. Once Approved, the LPA will not be coming along to inspect the works that are undertaken, unless perhaps there is a complaint from a neighbour that suggests some wrong doing.

 

Other LPA's, that are still resisting Class Q's, appear to be asking for SE calcs that determine the new loads into the existing structure and the SE's opinion on whether the existing structure can withstand those loads.

 

Within his blog it was Martin Goodall's stated view that although controversial, "up to a point, new foundations and/or underpinning may be acceptable".

 

Since you haven't yet purchased the property, it may not be worth taking the risk, without an SE confirming the existing slab can take the loads of the conversion.

 

Or, you could submit for a Certificate of Lawful Development and set out the works you intend to do and ask the LPA if they agree it is within the planning Approval.

 

The existing owner may not appreciate this route as a negative response from the LPA could nullify the planning approval.

 

Another option maybe to informally approach the LPA on the merit of a full planning application for a Change of Use conversion that uses the existing Class Q Approval as a back stop. This is the optimum scenario, and one that is now supported by successful Appeals.

 

Are you sure the existing barn structure sits on the slab? It's typical of a modern, portal frame structure to have individual foundation pads under each column, and maybe the slab is poured above this level with external walls, between the columns, sitting on that slab.

 

Quote

• The regulations do not allow the introduction of new foundations, loadbearing floor slabs or significant rebuilding works.

 

I think this must be a 3rd party's view on the legislation since it is not stated in the legislation that "the introduction of new foundations, loadbearing floor slabs or significant rebuilding works." are not allowed. I would not agree with this view.

Edited April 16, 2023 by IanR

[saveasteading]

A 200mm slab is very thick and unusual on a farm building. Has this been checked in the middle. The edges will be deeper perhaps giving the impression that the slab is thick.

 

Unless this is a pole barn, the columns will have concrete footings, tho unlikely to be to domestic standards.

 

[ChrisF8]

I’ve re-read the report and it states:

 

The building is constructed of wooden frames which are secured in a concrete floor which showed no signs of cracking. I was presented with a trial hole which concluded that the existing floor is approx 200mm of reinforced concrete.
The building consists of internal bays which vary in width. The roof is corrugated sheet metal and the surrounding sides are all black shiplap wooden boards.
On inspection the wooden frames are secured by concrete footings and cross members are treated timber and in good order. These showed no signs of deterioration and in my opinion will be sufficient to carry the weight of the proposed new alterations for a single storey conversion as shown in the sketched drawings.

 

I’m not totally convinced but the report as the company seems to no longer exist so I think I’ll get a second opinion. We’re likely to go for full planning anyway but only once we know we have the fallback position of Class Q so we can purchase the land. 

The barn is over 150 years old, I’m not sure on the construction type so have uploaded pics of the internal beams. 
 

Thanks everyone for your input 
 

 

[George]

Obviously only very minimal info there but that is a bit of a stretch for Class Q imo. 

[IanR]

1 hour ago, ChrisF8 said:

wooden frames which are secured in a concrete floor which showed no signs of cracking. I was presented with a trial hole which concluded that the existing floor is approx 200mm of reinforced concrete.
~~~~~
On inspection the wooden frames are secured by concrete footings and cross members are treated timber and in good order. These showed no signs of deterioration and in my opinion will be sufficient to carry the weight of the proposed new alterations for a single storey conversion as shown in the sketched drawings.

 

The mention of concrete footings suggest that there may be more than the 200mm RC slab, although at 150 years old it's unlikely to be the original foundation. If you can get an SE, engaged by you, to agree you're covered structurally.

 

But, It looks to me from the first image that the eaves are relatively low. Is the top of the concrete slab level with the bottom of those doors?

 

If you felt you had to use the existing slab, you are first going to need to get it level, if it's not already. Agricultural slabs will often have a fall on them to drain. If it's was built for animals then that fall may be quite significant. Once level you'll then need to build it up with insulation, a screed and your floor finishes. The Finished Floor Level is likely to be around 200mm above that levelled slab.

 

If you then work from the plane of the current corrugated sheeting, which under Class Q you can't exceed, you'll need at least 300mm - 350mm thickness to the inside of the plasterboard. Is there sufficient headroom left inside once you account for the layers that need to be added for the conversion?

Edited April 17, 2023 by IanR

[ChrisF8]

Yes the main barn is over 4 metered high high so plenty of headroom, cross section attached 

 

Edited April 17, 2023 by ChrisF8

[IanR]

29 minutes ago, ChrisF8 said:

Yes the main barn is over 4 metered high high so plenty of headroom, cross section attached 

 

 

 

It does look like you can squeeze in 2.4m to the bottom chord, but it needs some detailing around the eaves to squeeze out as much height as possible for the structure around window and door openings.  Ball park it looks as though structural openings could be around 2.2m, which is enough, but if another 100mm was lost in levelling the existing floor and estimating heights from a jpeg image then the sight lines through the window glass could start to be a little compromised. This also only accounts for approx. building regs floor insulation, you may want the FFL a little higher if you plan a higher energy performance than building regs.

[LSB]

14 hours ago, ChrisF8 said:

We need some advice with a piece of land we’re looking to purchase. It has a single storey barn on it with class q approval. On further inspection the barn is sitting on a 200mm concrete slab that I’m presuming wouldn’t pass building regs as suitable foundations…so we would need to underpin it.
 

my question is… is underpinning classified as ‘new foundations’ or it reinforcement of the existing slab? Either way does this invalidate the granted permission as the class q conditions state:

 

• The regulations do not allow the introduction of new foundations, loadbearing floor slabs or significant rebuilding works.

 

We are doing a class Q as Susie said and our SE said we need to underpin 75% of the existing walls, some as deep as 2.4m due to a patch of clay.

The depth decision is down to the building control man.

Currently we are digging the trenches for the 'not wall' i.e. there was never anything their and BC are coming Wed for 1st inspection and concrete (all being good) Thur.

Our LPA said NO, NO, NO to knock down and rebuild, even though there will be a house there.

The big paid with underpinning is that you can only do 1m at a time and our back wall is 25m long, so we have to do metre 1 & 4 & 7 & 10 etc., then 2 & 5 & 9  etc  so that the existing wall doesn't fall down.

We have current foundations of about 200 as well and the walls are totally solid and have been standing for 60 years, and we are only building single storey so it seems totally over the top.

 

So, in answer to your question, yes you can underpin barn walls, but it is a total 'pain in the ar**'

The difference for us is that we already owned the barn and land as part of our farm.

 

Good luck and shout if you need any more help.

 

 

[IanR]

17 minutes ago, LSB said:

So, in answer to your question, yes you can underpin barn walls, but it is a total 'pain in the ar**'

 

Was that clear on the Class Q planning submission? I know our LPA are happy with modified foundations, but a lot seem not to be.

[LSB]

2 hours ago, IanR said:

 

Was that clear on the Class Q planning submission? I know our LPA are happy with modified foundations, but a lot seem not to be.

We had to have something like 8 reports to get Class Q, one was a structural survey to say that the barn was structurally sound enough to be converted to a dwelling.

This survey said that some level of underpinning would be required due to the changed in Building Regulations.  This was a bit like buying a house where you can have a basic survey or the full bells and whistles one.

This first one was just to get planning which was issued with a number of conditions.

 

We then had to have the full bells and whistles with cream on top survey to get building regs approval to actually build.  This has taken about 2 years since planning was approved, largely because of Covid I will add.

It was this 2nd survey that specified all the details about foundation depth.

Ironically, the same company (different dept) also did our contamination survey, a condition of planning, and dug about 8 trial holes to check soil quality and for any gases, which had to be measured (on site) weekly for 3 months.

It is from these trial holes that the SE got the details of the soil, they never even attended site, but looked at geological maps of where clay is.

In fact in digging we have found much less than they said, only about 3m square in one corner and BR are happy for shallower trenches.  We still have to underpin though a bit at a time.

We are DIY self-builders so we are doing the conversion is about 5 phases and the first underpinning trials will be next week.

 

 

[Temp]

I wonder if you could find a private BCO who would give an opinion on the suitability of the slab (for a hours fee probably). 

[Glenn]

As someone pointed out higher in the thread, I like many others started out as Class Q and moved to full planning for more flexibility. OTOH, my build has some similarities in that it was a timber frame on top of a very thick slab with no foundation (1977 fruit cold store, thick slab for forklifts and apple crates). Some learnings for me:

1. SE mandated underpinning based on soil (clay) and trees close by. Your local condition may vary

2. The SE specified the usual 'Pour 1m of underpinning at a time, joining rods between sections poured'. I thought blow that, it's a thick slab with a light and stable timber structure sitting on it. Luckily ground workers agreed after pouring an exploratory corner and it was completed in about 4 pours

3. The groundwork crew had a 'double bucket' on the digger which minimised the amount of manual digging out (and hence cost) under the slab perimeter

Regards

Glenn

[saveasteading]

1 hour ago, Glenn said:

I thought blow that, it's a thick slab with a light and stable timber structure sitting on it. 

My 4 years at uni and then 4 years practical seems to have been a waste of time.

 

Seriously, that sort of chance is sometimes a gut feeling based on a feeling for the physics, that some peopld have, but often goes badly wrong.

I've seen plenty go wrong  fortunately usually other people's problems.

Happy for you that it worked, and the wind didn't blow.

[SteamyTea]

14 hours ago, saveasteading said:

My 4 years at uni and then 4 years practical seems to have been a waste of time.

Mine has been.  Chefs, and chalet cleaners earn more than environmental and renewable energy graduates.

 

[Dave Jones]

out of curiosity.

 

What is to prevent doing all the underpinning prior to implementing the planning permission, e.g. commencing building regs ?

 

Wouldn't that be permitted development ? A farmer can concrete floors, build internal walls etc without needing planning afterall.

[Glenn]

16 hours ago, saveasteading said:

My 4 years at uni and then 4 years practical seems to have been a waste of time.

 

Seriously, that sort of chance is sometimes a gut feeling based on a feeling for the physics, that some peopld have, but often goes badly wrong.

I've seen plenty go wrong  fortunately usually other people's problems.

Happy for you that it worked, and the wind didn't blow.

Sorry not to have sought your opinion before using my own experience (and the input of others, including the SE) to make what was at the time a rational, not risky decision.  All I was flagging up was the 1m pour at a time seems to me to be the default for everything, whether it be an 18thC barn sitting on brick dwarf walls or a 20thC redundant agricultural building. SEs naturally need to cover themselves, it's their reputation and livelihood on the line.

[saveasteading]

2 minutes ago, Glenn said:

including the SE

You didn't say that, in fact implied the opposite.

I read it that you were bragging that you ignored the advice.

I see a lot of that on less worthy discussion sites than BH and it worries me.

So perhaps I misread. I am all for sensible efficiency.

 

What was particular to your situation that allowed a 4m run of footing to defy gravity?

[Glenn]

13 minutes ago, saveasteading said:

You didn't say that, in fact implied the opposite.

I read it that you were bragging that you ignored the advice.

I see a lot of that on less worthy discussion sites than BH and it worries me.

So perhaps I misread. I am all for sensible efficiency.

 

What was particular to your situation that allowed a 4m run of footing to defy gravity?

Casual language equals bragging? Wow. Maybe I will stick to enjoying this forum (which I have learnt so much from) as a silent participant. Offering opinions and common experience seems a little fraught. (BTW, no mention of 4m pours)

[saveasteading]

I apologise.  It seems I  have misunderstood what you were saying, both times.

 

 

[Glenn]

Thanks you, truly appreciated. I in turn will endeavour to be less prickly (and more precise in my language)

[kandgmitchell]

Well George, got this one through as a Part Q. Remember, works inside a building are not development for the purposes of the Town and Country Planning Act.......

[Temp]

Might be hard to underpin from the inside though 🙂

[IanR]

9 minutes ago, kandgmitchell said:

Well George, got this one through as a Part Q.

 

Is it a poultry shed? What's the plan for the last few metres either side, where the headroom is a little restricted?