Re-forming blockwork nibs for new RSJ?

[chesh12]

Hello,

I have a 60's bungalow where an internal dividing 100mm blockwork wall of about 4m length was removed 15 years ago. (It was not load bearing but was built off footings as was the way for dividing walls those days). When it was removed the blockwork was cut flush and plastered over. There is currently just an empty loft above, but we are now thinking of moving water cylinder for heating etc to that area of the loft, so a structural engineer has suggested a new RSJ should go across, sited where the wall was, so we then build a timber platform partly off that.

SE has said a steel can either span into the side block walls (and sit on 100mm bearing on new padstone below) or sit onto new 250mm x 100mm blockwork nibs, being toothed back into the original side block walls, as the foundation is still there below. The nibs approach is not as clean looking but means a smaller and cheaper section RSJ can be used to span so that will be easier for us to fit. I have calcs for both approaches and am trying to choose between them..

My question is, would Building Control actually allow forming new 250mm long bwk nibs simply by toothing 100mm dense concrete blocks back into the original blockwork bond (and sitting the padstone on that)? I guess it's basically the same structurally as cutting an original wall back to leave a nib, but any advice on this idea please?

Thanks!

 

[cdbe]

Can't see the cost of a slightly longer, beefier steel being significant, possibly it would need the ends chamfering to fit in the eaves - to fit you'd normally remove a few roof tiles and slide it in. Better than building new nibs. Your SE should be designing any toothing in to be acceptable to BC. Would a few timber joists not be ok? Plenty of tanks in houses without steelwork.

 

[^woody^]

Building control don't and normally can't argue with an engineer's design.

Pay the cost of a no nib option - wait and save up if you have to, you'll regret it otherwise.

And put the beam above the ceiling if you can.

 

[chesh12]

Yes I think no nibs is best, and ideally above ceiling level. Engineer seems to be a man of relatively few words accompanying his calcs, but did give beams and pads details.

Its true the old cold water / gravity fed tank was on a timber frame braced off an old chimney stack up in the loft, but that chimney came out years ago and a mains pressure tank was then fitted in a room at ground level. This tank is being replaced and moved into the loft next to a new boiler also going up there.

Thankyou guys.