Lintel bearings

[colinbaisden]

HI,

I wonder if someone could make suitably informed comment on the following query regarding building regs.

My house had a small extention built (prior to my occupation) that extended the size of a downstairs room from 3mx3m to 3mx5m (approx). An opening was cut in the external walll of the existing room about

2.2m wide leaving two pillars of about 400mm on which two box lintels were mounted (one per wall leaf). These pillars make the room very difficult to use as a bedroom and I would like to reduce their size (or idealy completely remove them by replacing the box lintels with a cavity wall lintel.

I am wondering why these pillars were left so large in the first place as a 3.3m lintel could span the opening and sit on the perpedicular walls?? OK this would only give 100mm bearing depth but could a spreader be used to compensate for this as I have seen in cases where an RSJ is used? or worst case, why can't I reduce the pillars to 50mm giving me 150mm bearings? The wall does not carry floor load.

Many Thanks for helpful responses.

Cheers, Bert

[dg]

Lintels can have 100mm bearings.

dg

[colinbaisden]

My understanding was 100mm bearings were only applicable for spans of

1200mm or less?

[dg]

No. It is dependant on the reaction (load) at the bearing. In a standard domestic situation, a lintel or beam is OK for 100mm bearings.

It may be different if there are some specific point loadings near to, or lack of restraint at, the bearings.

dg

[colinbaisden]

ok mate, many Thanks

[somebody]

In message , [e-mail] writes

This really is a job for a structural engineer, but as a rule thumb, most lintels will sit on a 100mm bearing over a standard 112mm thick red brick - but it is just that, a rule of thumb.

In reality, the actual compressive strength of the material versus the ultimate load being taken on the lintel would usually dictate the bearing area.

Downwards force/load is the most oft quoted factor, but particularly on outside walls you may have to also take into account lateral/wind loading on the wall - hence the pillar. Consider simple garden walls which often incorporate pillars.

Hth Someone

[colinbaisden]

Well the wall in question is now an inside wall, at least for the first storey (single storey extention)?

[somebody]

[snip]

[snip]

Indeed :-) I am not an engineer but IIRC a typical figure for wind loading of an "average" house external wall is around 1kN/m2 (100Kg m2)

- but you need to add the roof wind loading as well.

If you add this up for the area above and beside the opening I wouldn't be surprised if you find total lateral loads in the range of tons, not Kgs. Obviously a typical house will also have internal walls and the roof structure which all help to 'tie' everything together.

I do really think you need to consult a Structural Engineer who can give you an absolute answer. You may find that using spreaders as you mentioned is appropriate, but personally I'd would want to know for certain before risking it :-)

Hth Someone