Garage Floor - Building Control

[JCB520]

Hi,

As you may have read from my previous questions, i'm currently building a 2 story extension. Ground floor garage with bedroom above.

We have just got upto damp course and are planning putting the garage floor in next.

For obvious reasons I want to put in a solid concrete slab for the garage floor. don't feel the expense and hassle of a beam and block is justified for a garage floor. However I live in a heavy clay area and when I dug out the ground for the oversite and built the footings, the area inside flooded from the rain, and did not drain away, as I said very heavy clay area, no drainage.

Building control saw this and said that he wants us to have a beam and block floor to prevent the risk of water rising through the floor (he thought the water was coming out of the ground and not the sky).

He then went on to say that if I took out an airbrick from the existing house then that will show that that is beam and block and would want to copy the existing design.

I have done this and sure enough where there is a room on the inside, there is a plastic channel which goes down into the cavity and I assume under the floor. Except the airbrick which is where the previous garage was (converted to dining room). This is just blocked up and goes nowhere.

Building control is coming out tomorrow to have a look and tell us what he thinks.

My question is this:-

Can he enforce us to have a suspended floor or would we be able to ignore his advice and go for the slab, and still get it signed off. I really don't think a beam and block is justifiable, especially as the previous garage obviously didn't have one.

I know its been a long winded explanation, but any help would be much appreciated.

Thanks
Dave

 

[noseall]

I have built many garage floors in Staffs and have never been asked to build b&b floors.

During one particular build in Tamworth, it rained frequently. Any hole dug more than 18" below the surface resulted in the hole filling with water! This occurred even when it was not raining. No mention of b&b floors.

However there is a high risk of large volume changes regarding water content within clay soils. Dessicated clay shrinks, saturated clay swells.

are there any trees or large shrubs close by?

 

[JCB520]

There are a row of leylandi about 5 meters away from one of the corners.

We had to dig down and put in 2 meter deep foundations to prevent root invasion they said (5 meters, as if!) but this had nothing to do with heaving and shrinkage of the clay.

Surely though if the rain water cannot drain away because of the hard clay, then any ground water won't be able to come up?

 

[noseall]

then any ground water won't be able to come up?

I must admit, it does seem an odd reason (the risk of water springing up through the slab) for b&b floors. More in common with clay heave/shrinkage though.

Even so, i'm pretty sure it will be precautionary and not enforceable..

 

[JCB520]

Thanks for the advice.

The reason he gave behind it was water / damp invasion and not that the slab could be prone to movement from clay heave / shrinkage.
He only bought this up because of the amount of water he could see sat on top of the clay.

I will let you know how I go on.

Again thanks
Dave

 

[JCB520]

ok update.

Building control came round and had a constructive debate (ha ha) with him.

He eventually relented and agreed that a suspended floor was overkill for a garage, BUT......

Because the existing airbricks would now be inside the garage he insisted that I fit ducting under my new solid floor and through the new side wall to a new airbrick, to give the existing suspended floor ventilation. Due to the fact that the existing airbricks would have now been inside a garage, he was very wary about fumes from exhausts getting under the house floor. Fair point.

So I have had to raise my garage floor level and remove bricks below the existing airbricks to fit a duct direct into the underfloor void and channel it across where my new floor is going using 110mm soil pipe, and into the new cavity wall, where I have fitted a telescopic vent to bring it upto DPC and a new airbrick.
I have had to do this for 2 existing airbricks.

Hopefully this will satisfy him (he's coming out to have a look this week) and I can get my floor down.

Just a bit of info for anyone interested, I had a nightmare finding the adapters to go from a brick sized rectangle to a 110mm round pipe (apparently they don't do a rectangular channel)

Eventually tracked some down. Travis had to order then specially. They are made by a company called Manthorpe and they cost £10 each.

Thanks to noseall for the advice.

I'll keep you posted on the progress of the extension.

Dave

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• JCB520
• 22 Mar 2009
• 1

Untitled

• JCB520
• 22 Mar 2009
• 1

Untitled

• JCB520
• 22 Mar 2009
• 1

 

[noseall]

Just a bit of info for anyone interested, I had a nightmare finding the adapters to go from a brick sized rectangle to a 110mm round pipe (apparently they don't do a rectangular channel)

Eventually tracked some down. Travis had to order then specially. They are made by a company called Manthorpe and they cost £10 each.

The last time i did this, i warmed the end of the pipe with a blowlamp and shaped the pipe to suit using two bits of 2" thick timber and a bit of stretching. No kidding. Worked too. You do need to keep the flame moving though.

 

[RobinClay]

I had a similar challenge with "adaptors" for an extractor fan duct in my case, two rectangular ducts (to avoid the diagonal bracing between floor joists) going into a length of 110mm soil pipe laid between the floor joists. I cut a large plastic milk bottle to suit, and warmed it with a hot-air gun and stretched it to fit. And then wrapped the whole lot in duct tape. The soil pipe was fed through a hole in the outside wall, and an extractor fan was fitted into the end of the soil pipe. Crude, but effective.

 

[festive]

This is great, thanks for sharing just what i was looking for.

Here is the detail for it on their website:

http://www.manthorpe.co.uk/Building/Products/Through-Wall-Underfloor-Vents/Remote-Void-Vent.html