Foundations Questions

[boycey9]

Hi Guys,

Building a single storey extension in 215 blocks and
Looking for a few answers to help me understand things better before going ahead with Builder.

I have been given the go ahead to use a lintel over the drain that runs along the back of the house between the existing foundations and the new.
The lintel will be 1.5 Metres long to bridge the Gap and width big enough to take the 215 blocks I am using.

However the Existing foundations were not exposed when I had the visit and upon exposing them I find they are Maximum 150mm out from house but are quite rough and bumpy. Is this ok or do I need to get the Inspector back now its exposed.
House was built in 1930's not sure if this is normal, Can I grind them flat.
There is signs of pebble dash so maybe its just this and ok to chip back?

Also If ok to proceed how is the existing foundation brought up to level with the New, its to large a gap for Mortar.

 

[boycey9]

Ive answered the first part myself, It was just mortar and stuff from the original pebble dashing, Once I cleaned it up a bit more I could see a join and gave it a wack so happy days.

Although still interested to Know how to make up the difference in height between the two foundation old and new. The difference is about 200mm.
Can I use a trench block or do I need a pad stone or something like that.

 

[PaulJR]

It's going to see a quite concentrated load - the weight of half the wall on the lintel (almost) so for the small cost involved I would suggest some sort of padstone carefully bedded on a strong (3:1) sand cement mortar.

Make it wider than the lintel - as wide each side of the lintel as it is deep, so if it is ~200mm deep make it at least 615 - this will spread the added load out along the existing foundation. You can probably find something in standard PCC lintels that will do the job.

 

[PaulJR]

Ignore that - I have just realised that it's the new foundation that's deeper .

I assume that the new walls are going to be set to course into the old?

If so you should be able to build up the level with trench blocks without any hassle.

It would be worth putting some sort of spreader onto the existing footing though, just to be sure.......

 

[^woody^]

Ignore foundations differing in levels.

Gauge down from the DPC and get your masonry to work to the gauge. If you do need a cut or split course, put that on the foundation which will require the fewest cuts - which will normally be the existing one