Using a lintel as a foundation

[Carlnorwich]

I am going to convert my garage to a bedroom. This means I will need to remove the garage door, block the opening to half way and have a new window fitted.

I have been told that I should dig a shallow foundation and then fix a couple of lintels into the ground, then build the blocks off these.

Has anyone done this before? The garage door opening is 2000 wide. Can I buy a lintel that is exactly 2000 wide?

Many thanks.

 

[^woody^]

The lintels span the opening, and are not just dropped onto the ground

 

[regsmyth]

That sounds like strange advice. I never realised this was a common way of preparing footings. Who gave it to you? They should also advise the section size (eg 100 x 150 etc etc).
Presumably they mean concrete lintels, and at 2m long, you might not be able to lift it on your own.

I guess it could be ok, but I think you need to ask for a bit more info.
Perhaps they mean to pour a couple of pads at each end of the opening, then to lay the lintels on them.
You might get them just the right length, or you might need a 9" grinder to cut them to length.

 

[^woody^]

The lintel spans the opening at the bottom of the wall just like it would do above a window

 

[JohnD]

if you use an ordinary lintel under an opening, you have to turn it upside down.

this is because a lintel over an opening takes the weight of the wall above, and passes it down the ends. A sill under an opening takes the loads through the ends and spreads them onto the wall or footing below. This prevents cracking under windows due to unequal loading.

Precast sills are made with the reinforcement the right way up already.

but I can't see why you don't just dig a trench and pour your own ground beam.

 

[Shytalkz]

Eh? Balancing a Cougar on its head would take some artistry

The loading to the lintel is not upwards all of a sudden. Or are you talking about it being on the ground as a sort of faux spreader directly below the window? Either way, the footing at either end of the opening will project beyond the reveals, so sit a lintel on there and span it across, then build up off that. Stick some helibar or brickforce in the joints if you must, but I really can't see that there is a problem with loads from above, on a garage conversion.

 

[^woody^]

if you use an ordinary lintel under an opening, you have to turn it upside down.

No, the lintel is supporting the same amount of brickwork just like it would be at 1st, 2nd or any other floor level, so you put it in just the same.

You would put a lintel in (well 2 lintels at £10) each instead of digging out over 2m3 of soil and digging down to 1m, disposing of it all and then filling with £150 worth of concrete.

 

[Shytalkz]

^^what he says^^

 

[archconsult]

Why on earth not just dig a tench to the same depth as the present footing of the garage and fill with concrete! I cannot see what is gained by using this alien form of foundation. I have designed foundations which span from concrete pad to concrete pad where drains have to be built over or where deep footings would undermine adjacent buildings but to dig a foundation and put lintels in as a basis for walling is not good practice in my view.

Firstly if lintels are used they should be built into or span onto the wall footings each end as otherwise they could sink down and cracks occur in the new walling where it meets the old. If you use lintels in this manner they should be reinforced concrete not the thin prestressed type with one stressed bar in.

The door span is likely to be in the region of 2.4 metres I imagine.

In my view you should just dig a trench to the bottom of the adjacent foundations of the present garage and fill the trench ensuring that the new concrete is higher and this sits on the present concrete. This ensures a good foundation for a new wall and reduces the chance of walling cracks over.

 

[^woody^]

Two things ... costs and time

And its a garage door opening, not the Petronas Towers, so there is no need to go to the extreme

I built mine (and others) off the front of the garage floor slab (which is 100mm thick) and threw some ex-met into a couple of courses to form a brickwork beam for good measure.

 

[Shytalkz]

Bloody architects, over-speccing again, eh, Woodster

 

[Shytalkz]

I cannot see what is gained by using this alien form of foundation. I have designed foundations which span from concrete pad to concrete pad where drains have to be built over or where deep footings would undermine adjacent buildings but to dig a foundation and put lintels in as a basis for walling is not good practice in my view.

What's the difference between your two scenarios and this? We (as in Woody and myself) weren't talking about putting them on the ground, but spanning them between foundations and/or walls. Like a lintel. The level it's at is immaterial, it's still a lintel. There's nothing wrong with the psc variant, providing that they're adequate for the load, which, placed at the bottom, they probably would be, if the wall above can arch below dpc level; and, if not, as before, bang some bed joint rebar in and make a composite beam.

 

[PaulJR]

I built mine (and others) off the front of the garage floor slab (which is 100mm thick) and threw some ex-met into a couple of courses to form a brickwork beam for good measure.

Agreed - its only supporting about a metre of masonry, just build it.

 

[Carlnorwich]

Thanks for your advice.

The lintel idea is favourite (saving time and money) Building control will need to approve it, so I'll soon find out their thoughts - which will setlle the debate.

Thanks again.

 

[^woody^]

.... so I'll soon find out their thoughts - which will setlle the debate.

Or most likely start another