Foundations Ideas

[BoltonPete]

Hi would appreciate thoughts on how to go about approaching some foundations.

We are looking to build a small extension to the rear of our 1980's built end townhouse. Plan is a 3m x 3m extension built using a SIPs kit. I would like to get the foundations in so I can then get the exact dimensions to the SIP kit manufacturers.

Original thought was to sdo some concrete pads, build some brick piers and then use block and beam to create a solid base for the SIP kit. Today have been doing some investagory holes and have found a couple of issues. Firstly we have a shared drain that runs across the location of the extension, this is in good condition and is about 1.5m below the ground level.

Secondly, despite digging down about 4ft we have not been able to find solid ground.

If I understand right, building regs requires that the foundations extend down futher than the drain for it to span over. concious though that for a relatively light weight small extension this could lead to a lot digging and concrete so trying to consider other ideas.

Thoughts are the moment would be to use ground screws down to a depth lower than the drain, then use timber joinsts to create the base for the SIP kit. Not sure how receptive Bulding Control are to the use of ground screws though.

Further throughts appreciated!.

Thannks, Pete

 

[freddiemercurystwin]

It's unlikely your water company (who you will need to approve the proposals) will approve anything other than foundations deeper than your drain. Foundation design is indifferent as to whether you have a single/double storey/traditional/timber frame or SIPs extension. If you vear away from anything traditional (ie strip foundations) you'll likely require a structural engineer to design them. BTW as a build-over will be required you'll need to do a full plans building regs application and have your build-over approved before you start on site. SIPs for domestic extensions are often no more economical after everything, though perhaps with material costs going the way they have they are more viable now, they are certainly far more difficult to extend or modify in the future.

 

[BoltonPete]

Hi thanks, yes, we have had full plans drawn up. At the time the architectual tech that put them togeher deemed that the pad foundations then connected by the block and beam system should be sufficient as they essentaily bridge over put no additional stress on the drain. However at the time of design we had not explored how deep the drain was as it was an unknown until some exploratory digging had taken place.

Wondering also is mini-piles under the pads might solve the problem?

Going for SIPs as I want to do as much as possible myself and its in my skills set, unlike brickwork!