Foundations for Concrete Block Walls

[hmpmarketing]

Hey all, me again

 

Have decided to go "DIY" route with my garden office, after chasing so many people, absurd quotes and people not really bothered to get back to you when may potentially be a client, I think I will do most the work myself except for the specialised bits like electrics, doors, windows.  A brickie mate of mine will lend a helping hand laying the 4 concrete block walls, and the last bit, foundations.

 

On a previous thread, I had asked about an initial query with the B.C. that was responsible with my house build regarding the foundations for this building (I didnt even mention what materials I would use for the walls) and his reply was:

 

"If the building was a garage the proposed footings would suffice, if the building is for another use full strip footings of at least 1 metre depth are required."

 

I think this is really over the requirements, or is he correct?

 

It would be 2 walls of 6m and 2 of 8m in length, 2.7m high probably

 

Thanks again everyone!

 

 

Edited August 10, 2018 by hmpmarketing

[Declan52]

It would be up to you to prove that Foundations that are 400mm,500mm,600mm deep etc are adequate by getting proper calculations done by a structural engineer. 

[nod]

1 hour ago, Declan52 said:

It would be up to you to prove that Foundations that are 400mm,500mm,600mm deep etc are adequate by getting proper calculations done by a structural engineer. 

It’s also a lot of exspence when your building starts to move 

On a structure of that size a few mtrs of extra concrete isn’t that exspensive 

[hmpmarketing]

I may as well get my Structural Engineer involved then

[Oz07]

Correct me if I'm wrong but in England building control have no interest in anything under 30m2 internal. 

 

Build it off what you like in this case, even topsoil! This is where a good builder might help you. If you hit good ground 500mm down, and your house is only on similar footings in a similar location why go down to 1m. 

[Ian]

@Oz07 +1

@hmpmarketing in England it's called a Class 6 exemption for small detached buildings. As @Oz07 said, the building needs to have an internal floor area not exceeding 30 sq.m and there are some other limits listed here: http://www.legislation.gov.uk/uksi/2010/2214/schedule/2/part/6/made

Unfortunately, it sounds from your description that the building is a little larger than this.

 

Edited August 10, 2018 by Ian

[Mr Punter]

If it was me and planning consent is not needed I would not involve BC.  I would want to dig down to a reliable base for my foundations though.  Deeper foundations cost a fair bit in muckaway and concrete, so if it is only for an annex I would do as little as pos.  When / if you come to sell you can do the "purchaser must rely on their own enquiries" as to whether BC was required / applied for.  Mortgage lender will only be interested in the main house as security.

[hmpmarketing]

Hey guys, thanks for the feedback, yes I go over the 30m2 rule, so B.C is required.

 

I am just trying to find the most affordable foundation method without spending so much, I was just trying to understand why with no specs of the wall fabrication, the BC officer said I had to go 1m deep. I have not commissioned him yet to do the work (he was only involved in my house BC) . I just cant believe walls of concrete Blocks 225mm x 450mm, 2.7m high would need to go this deep.... just trying to find other people's experience with this

 

My plan is to hire a ready mix and pour myself with my builder friend (he will build the frame for the concrete pour) just trying to find the affordable way but still go wit the rules!

Edited August 10, 2018 by hmpmarketing

[Mr Punter]

If ground conditions allow, I like the concept of insulated slab foundation.

[Declan52]

Will this always be a garden office or in the future could you end up using it as a granny flat type unit???

There are some real nice wooden ready made type buildings that will tick the garden office look. They won't require proper foundations. 

But if it could end up the other option in later years then get the calculations done and see how far you need to go down and when the time comes you will be able to prove that only going Xmm deep is adequate.

[ProDave]

If it is a garden office, the last thing I would be building it from is blocks.  I would want a well insulated timber framed construction, which as I am sure we have discussed many times, could very easily be built as a portable building so exempt from building control.

[hmpmarketing]

2 minutes ago, ProDave said:

If it is a garden office, the last thing I would be building it from is blocks.  I would want a well insulated timber framed construction, which as I am sure we have discussed many times, could very easily be built as a portable building so exempt from building control.

 

Hi @ProDave,

 

I have definitely taken the mobile route into consideration (from the previous thread), but I find it hard for me to build a structure myself that would satisfy the council as a mobile structure.  The ones I have chased are quoting really absurd prices for the size I need to go with.

 

Also to build it myself in timber would be much harder as I have my brickie mate to do the work nearly free.... will be insulating the block wall internally of course.

 

 

 

 

[hmpmarketing]

17 minutes ago, Declan52 said:

Will this always be a garden office or in the future could you end up using it as a granny flat type unit???

 

We could convert this into a type unit in the future.

[Declan52]

3 minutes ago, hmpmarketing said:

.. will be insulating the block wall internally of course.

 

 

 

 

 

Is this going to be single skin block build or a cavity??

[hmpmarketing]

2 minutes ago, Declan52 said:

 

Is this going to be single skin block build or a cavity??

 Single skin 

[Declan52]

Is it not better to use external wall insulation then as you will be making the inside smaller.

[hmpmarketing]

57 minutes ago, Declan52 said:

Is it not better to use external wall insulation then as you will be making the inside smaller.

The actual dimensions would be 8.36 x 6.26, so I got some room for sure

[Declan52]

1 minute ago, hmpmarketing said:

The actual dimensions would be 8.36 x 6.26, so I got some room for sure

That's a big office/granny flat.

[hmpmarketing]

On 10/08/2018 at 16:13, Declan52 said:

That's a big office/granny flat.

Hi, away for the weekend.

 

Yea, future plan is to convert this into a 1-bed, hence the need for concrete walls initially

[epsilonGreedy]

On 10/08/2018 at 09:40, Declan52 said:

It would be up to you to prove that Foundations that are 400mm,500mm,600mm deep etc are adequate by getting proper calculations done by a structural engineer. 

 

 

I thought the opposite was true i.e. Building Control should explain why default foundation minimums are insufficient in this specific case.

 

My building control inspector told me that my plan for a 600mm x 600mm concrete pour was in excess of mandatory minimums after he had inspected my dug trenches and examined the sub soil type.

Edited August 22, 2018 by epsilonGreedy

[PeterW]

16 minutes ago, epsilonGreedy said:

 

I thought the opposite was true i.e. Building Control should explain why default foundation minimums are insufficient in this specific case.

 

My building control inspector told me that my plan for a 600mm x 600mm concrete pour was in excess of mandatory minimums after he had inspected my dug trenches and examined the sub soil type.

 

Unfortunately this depends on your BCO as much as anything - the minimum for a strip foundation in firm sand is 250mm which is why your BCO said it was ok. What you’ve ended up with is more than a strip and less than trench fill which is perfectly acceptable. 

 

The bigger issue is that BCOs accept no liability for structural failures so if they get it wrong then you have no legal recourse...

[Declan52]

It was the building control officer who has wanted it to be 1m deep. The only way you will be able to change his mind will be with hard facts on paper. Saying to him my mate 2 doors up only went 500mm down won't cut it. 

My founds are only 225mm deep but they sit on very very hard boulder clay so won't go anywhere. Could have built straight of the clay it's that hard.

[epsilonGreedy]

8 minutes ago, Declan52 said:

It was the building control officer who has wanted it to be 1m deep.

 

 

Well yes I think we all accept this basic fact. My point is that when demanding more than standard minimums is the BCO obligated to explain why? I guess he did but the OP does not have the experience to recognize the trade language.

 

I acted as brickie's mate to two pro brick layers the other week and encountered a new strange language.

[Ed Davies]

Reminds me of the story of the little girl helping out the brickies building an extension on her parents' house: she'd been bringing bricks round the side of the house in her toy pram. At the end of the week, as she'd actually been a bit useful, when they got their wage packets they'd clubbed together to give her some pocket money “wages”.

 

Her mother was amused by this and asked if she was going to be working on the site next week. “Yes, if we can get the fucking bricks”. “Umm, maybe not”, says Mum.

[Cpd]

8 hours ago, Ed Davies said:

“Yes, if we can get the fucking bricks”.

Kids.... off topic but..... we don’t have a TV..... our kids were round at a friends farm house, all the other kids were watching the Tv my ones trooped in looked at it for a few seconds and trooped back outside where I was talking to the farmer. “What’s on TV I asked ?” ‘Bull shit dad” and off they went........ I love that my 3 year old knows how to use a bit of quality language in the right context.