Loft conversion Steel on top of wall plate

[bob1651]

Hi. I am planning a loft conversion and have all the plans and calculations completed. My home is made from brick outer skin and thermalite (v soft) block internally. My calcs have been based upon steel work (which will support the roof and new floor) on top of padstone or steel spreader plate which will then bear onto the soft block inner skin which requires me cutting out the timber wall plate and the softblock below.

I was wondering if I could leave the timber wall plate in situ and put the steel spreader plate on top of this instead due to the timber appearing much stronger than the soft block below.

It seems a much simpler solution and requires much less work to install the padstone in a confined space. The softblock even with padstone or steel plate is concerning me.

Thanks

 

[noseall]

The steel should sit directly upon masonry and not timber.

 

[bob1651]

Thanks Noseall, can you elaborate why not too. I have since contacted my building inspector who will have no objection if I put the Steel on to the timber via a 600mm x 10mm steel plate or even a C section that will clip over the timber. And my building surveyor also says it can be done. The only thing everyone says is they would prefer not too but no one is giving me a reason why. My concern is that I am likely to make the padstone on softblock unstable whilst moving the steel around for position and the steels will only bear on one block at a time. My experience of soft block is they dont bond very well especially the top course.

 

[noseall]

The obvious reason is volume changes within the timber. The last thing i would advise is to lay something as important as structural steel upon timber.

That said timber joists and wall plates bear a fair load and eventually stabilize once the initial drying out has occurred.

I would be more comfortable with masonry simply because of the concentration of weight upon timber, i.e. point loading.