I am building a garage but the footing will run over a 4 inch soil pipe running to the sewer. I guess the soil pipe is about 1 metre below ground and I require a 1 m footing. I am told I can go over the soil pipe but I may need to dig below it and then allow movement for the pipe to move ( perhaps by wrapping it in some insulation fibreglass). but digging below so the weight of strip footing is on virgin soil below, hence the concrete will run below it, but won't touch the pipe as the pipe is wrapped in fibreglass to allow it to flex. Is there anything else I should consider..The garage floor will be conventional concrete not beam and block. The footing will be inspected by building control but I am trying to think ahead. Many thanks.. Tolly
BC generally get involved with garages attached to houses or if floor area greater than 30 sq metres.
Don't take this as fact until checked out, but I think I heard about someone using pre-stressed concrete lintels to span over an underground pipe in just your type of situation.
Thanks for you comments..Just in case anyone else has the same issue.... I checked with Building Control (Suffolk area) and there are two preferred methods, The one I used and preferred by most building inspectors here, is to make a jab lite box. As my pipes were around 1m below ground level I had a 1m strip footing when the footing was dug out it left the exposed soil pipe on the floor of the strip footing. The gravel base was left in tact ( to support bottom of pipe) and then I formed a jablight (low density polystrene) side along each side of the pipe, ( used two peices to jablite as my jab was only 40mm so I had 80mm jablite each side of the pipe, then cut two pieces on the top to create a box. Before putting the lid on I did just put more pea shingle around the pipe. The lid was secured with a couple of small battens each side and another over the top. ( in the shap of a large staple over the top) so the lid or sides didnt move when filled with concrete/cement. The other method suggested ( by Building control) probabaly more suitable if pipe is higher in footing, Is to wrap the pipe in a fibreglass insulation then sleeve it with a larger pipe, e.g sleeve the 10mm pipe with a 150mm. this method would allow liquid concrete to run under the pipe unlike the top method where the pipe sits on the floor of the footing. No lintels were suggested in footings, although Lintels and normally used where a soil pipe runs thro brick or blockwork. Hence this could be below DPC but above footing, Or if you replaced some of the upper strip footing with trench blocks. Hope this helps Tolly
What I did for my extension and was approved by BC was. Dig trench to required depth which exposed the sewer pipe. I left the soil under the pipe undisturbed thus supporting the pipe in the same way it always had. Built a shutter on either side of the pipe and back filled with soil over the pipe. Poured the footings and then spanned the pipe area with a concrete lintle laid as part of the first course of engineering bricks.
Step the footing under the pipe and then use spanlite lintels above the pipe to carry the brickwork. If you are concerned about disturbing the existing pipe as you excavate beneath it, use Mr Kiplings method, with one additional suggestion Excavate up to both sides of the pipe, shutter round it with 2 side pieces and a lid and include some mesh reinforcement over the top extending a good 300mm past either side of the shuttering Main thing is to let BC know what your intentions are and get their approval
Also, as I understand it, if the pipe runs underneath the floor slab it is supposed to be encased in concrete. Thats one of the reasons I beamed and blocked my floor. In the end it cost no more than slabbing.
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