Dormer alteration steelwork for floor.

[Stuart.H.]

Hope someone can answer the query.
I understand the steel required for the ridge, as this is where the dormer will hang from.
Why do we need steels for the floor joists when there are brick walls upstairs for them to rest on?

Many thanks.

 

[freddiemercurystwin]

It's always better to start a new thread and post any architects or engineers drawings you have. Anyway typically in an existing roof where purlins are supporting rafters, two steels are fitted at floor level, one each side and a timber structural wall is built up off each steel beam up to the underside of the purlins, then any struts or other structural members inside the loft space can safely be removed.

 

[Stuart.H.]

Just wondering why we require steel in the floor of a new dormer.
The walls upstairs are all brickwork.
They do require shortening by 30cm, but the rooms are really tall so plenty of space.
The beam at the back of the dormer doesn't appear to be supporting anything.
The one under the ridge beam I guess supports something but not sure what.
Any suggestions?

 

[freddiemercurystwin]

Your steel on the RHS is supporting the rafters, your steel at the ridge is taking the top of the rafters and the rear of the dormer, without seeing the plan I'd hazard the steel in the middle is trimming the stair openings, is the dormer the full width of the house? You got any structural plans/sections from your structural engineer? Is that drawing done by your architect/designer, it's a bit crap.

 

[Stuart.H.]

Thank you for a prompt reply.
screen grab from the structural chap.
Understand the ridge beam steel, as it is needed because the dormer hangs from it.
Why do I need another steel to support on the RHS ? If it is for supporting the rafters, why can't we make use of whatever is supporting the rafters currently?
This is the dormer design once completed, sorry, not got the architects piccies handy. Again from the structural chap.
The floor beam doesn't align with the stairs. And if it is for the floor joists, why can't we support them on the current brick walls?
Unfortunately there is no mid level graphic, just the ground floor and the dormer, and not the 1st floor showing the walls.

 

[freddiemercurystwin]

My comments in red.

Thank you for a prompt reply.
screen grab from the structural chap.
Understand the ridge beam steel, as it is needed because the dormer hangs from it.
Why do I need another steel to support on the RHS ? If it is for supporting the rafters, why can't we make use of whatever is supporting the rafters currently? Because presumably your existing loft has various ties or struts that currently hold up a purlin(?), to be able to remove these struts/ties etc and be able to open up the loft space a steel beam is required to replace those existing supports.
This is the dormer design once completed, sorry, not got the architects piccies handy. Again from the structural chap.
The floor beam doesn't align with the stairs. You need to find out because at the moment it looks like the beam will get in the way when you walk up the stairs? And if it is for the floor joists, why can't we support them on the current brick walls? Are the brick walls structural - do they go all the way down to the ground? Do they have a foundation underneath them? If you don't know then your designer should. Do you actually have a designer? Or are you just using an SE? I've never seen such amatuerish draiwngs from an SE.
Unfortunately there is no mid level graphic, just the ground floor and the dormer, and not the 1st floor showing the walls.

Got a photo or two of the inside of your loft?

 

[Stuart.H.]

Marked out where there are currently big thick joists holding the roof up. These are also on the other side too.
This is from the room below looking towards where the dormer will be.
So my thoughts being that the current lower joist would carry on holding the roof up, rather than a new piece of metalwork at ceiling level.
The second picture is the room at the back where the dormer will be above.
All walls here are brick.

 

[freddiemercurystwin]

Need a photo inside the loft, can't make out anything from underneath. You need to answer the questions too.

 

[Stuart.H.]

Apologies, missed the Qs
Purlins are from wall to wall across the loft space, not supported by anything other than the brickworks.
So the steel at the back, the one on the right would be under a current purlin, so why would it be needed, as there is nothing supporting the purlin currently, beyond the walls at either end.
The upstairs walls align with the downstairs walls, though I get your point regards the foundations beneath. The current ceiling joists are not full length, they are 2 pieces joined together and supported by the wall.

The floor beam doesn't align with the stairs. You need to find out because at the moment it looks like the beam will get in the way when you walk up the stairs. No the stairs are going down from the door end (near the loo) so the steel would be over your head as you get to the lower end of the stairs, so not supporting stairs or anything like that.

Let me grab some piccies from inside the loft, each end of the current purlin and you may get a better idea from the view points. May be a day or two.
Thank for your help so far.

 

[freddiemercurystwin]

OK it's pretty rare for there to be nothing but a purlin with no additional supports, anyway you probably still need a steel in the floor to support the end of the new floor joists. Also the existing roof is gonna have some insulation and plasterboard hanging off it so having the steel there allows the engineer to avoid having to guess what/if any extra loads the existing purlin can or cannot cope with.

 

[stevie888]

The sad fact of the matter is that some SEs just shove steel in left and right without thinking.

I once redesigned a loft after 2 builders had refused to price the original which had 1.5 tonnes of steel in with a single piece weighing 750kg!! Tge design had been approved by the LA and the layout was dire, worse the stairs didn't work. (This last point should have been picked up, not LA responsibility to tell peeps the design is OTT)

My design wound up with a single 45kg bit

 

[Stuart.H.]

Update: From the ridge to the walls there are 2 purlins.
Each purlin is supported in the brick wall at each end.
I am making the assumption that the pieces of wood attached to the purlin is for holding the ceiling joists up rather than supporting the purlin.
All upstairs walls are brick and of solid construction, mortar is fine. ( we removed some plaster to confirm).
Maximum length for a new joist would be about 4m which is the distance from the window wall to the opposite wall in the back bedroom. Though guessing the chap is suggesting the span to be 3450 + 3450.