Concrete or Steel Cavity Lintels Above Window and Bifold Doors? Information, help and advice on many architecture, self build and design problems and issues

[manningcarl]

Hi, I'm planning to replace an old flat roof and windows on a small extension at the rear of my house. I've had conflicting "advice" on one aspect, which lintels to use.

The extension is double skin thermalite blocks with an insulated 50 mm cavity. Wall A is completely blocks.
Wall B will have 1 m high block work with a large aluminium window (1750 W x 1250 H) on top
Wall C will have 25cm pillars either side with central aluminum bifold doors ( 2500 W x 2200 H)
Wall D is the old external wall of my house.

The roof will be a flat roof (unsure on warm or cold insulation, that's another topic) it will have a parapet wall all the way round of 1 course of 9" thermalite blocks capped with stones.


My question is What lintels can / should i use above the window and bifold doors. Concrete or Steel Cavity Lintel?

Also on another note, with the works above do i need to notify the council to "replace" this existing roof. Its slightly different as the current one doesn't have the parapet wall. One builder said i didnt have to another said i did.

Thanks

[manningcarl]

any one?

[Mad110]

There's a company called IG LINTELS that supply long pressed steel lintels to suit just about any wall thickness. As long as you have 150mm bearing on each end and it's only a single storey building, their product guide ( I found it online.)will point you in the right direction. Buildbase and Travis Perkins usually have them in stock upto 3metres long.
These lintels also provide a good base for a cavity tray above the doors/windows.
I used a 3.6m long lintel above aluminium bifold doors without any problems.

[Mad110]

Ref: notifying building control,
If you're forming new window and door openings in a dwelling there are restrictions on the amount of glazing area, not sure of exact figure.
And if you go for a cold flat roof they'll want provision for 'cross ventilation' if it's the roof of an extension.

[manningcarl]

hi mad110

thanks for your reply,

i may not have been clear in my post. The current timber glazing is being replaced by aluminium. theres no new glazing.

Thanks for the info on cross ventilation, ill check on that.
Do you have any thoughts on the lintels?

[Mad110]

Yes, my first post was about IG Lintels from buildbase or travis Perkins.

[manningcarl]

hi thanks alot mad,

appologies i didnt see that post! :)