Loft Conversion Help - Roof Support

[bfrost99]

Hi guys first time poster on here so go easy!

I'm planning on having a loft conversion done and would like to do a few bits myself. I've done plenty of DIY around the house so I'm fairly confident but this would be my first major structurally related job.

So in my loft (mid-terraced property around 1800's) there's a purlin either side of the property with a supporting piece that joins to the joists below. Would it be possible to install supporting beams on each / every other rafter that goes straight down to square out the room instead of the purlin? Or would this create too much stress on the joists below?

I've done a sketch to try explain what I mean. I understand that the diagonal brace is that way as to support the load of the roof in that direction so the proposed idea wouldn't be as far back as I've drawn. The idea is to create a bit more room and so I can insulate and plasterboard it. The next question is about floor joists. So I've watched a few videos on loft conversions in terraced properties and for the floor joists I was thinking about tieing them to either side of the walls parallel to the current joists but raised say 30mm to then be able to put boarding down for the floor.

Any help or criticism on my idea for this would be greatly appreciated, thank you.

 

[Wayners]

Structural engineer and architect will draw plans.
Probably need steels made and fitted.
Have you approached architect?

 

[Harry Bloomfield]

That almost vertical, thick timber, is to help support that long horizontal span - it will transfer the load to the top of an internal, structural wall. Do not even consider disturbing that timber. Rather than your red pieces of timber being under a compressive load, they need to be designed to be under tension. They would be under the tension of any load you added to the loft floor.

 

[bfrost99]

I've not approached and architect yet as this is just sort of an idea at the moment. I just wanted to put my idea out there and see how feasible it was. Thanks for the information guys. As for the red timber, would they be under more of a tensile load then due to supporting the weight of the floor?

 

[Wayners]

Move out
Put stuff in storage
Take roof off.
Remove lath and plaster ceilings.
Drop new roof trusses on with crane ready made.
Roof and tiles would be back on in a week.

 

[Harry Bloomfield]

As for the red timber, would they be under more of a tensile load then due to supporting the weight of the floor?

Yes, they would be hangers. Your roof is much more rigid, than the loft floor timbers.

 

[freddiemercurystwin]

Typically in a loft conversion a steel beam is fitted each side directly beneath each purlin, spanning from party wall to party wall, then new floor joists are suspended between each steel and a timber supporting wall is built above each steel to support the purlins, then the struts can be removed eg

 

[Murdochcat]

And don’t forget you’ll need party wall agreements with BOTH of your neighbours - at your cost

 

[bfrost99]

And don’t forget you’ll need party wall agreements with BOTH of your neighbours - at your cost

Is that something you'd have to consider regardless of who carries out the work?

 

[Murdochcat]

Is that something you'd have to consider regardless of who carries out the work?

Er yes

 

[freddiemercurystwin]

Though they're not mandatory. It should be said I'm not sure what Wayner's last post or Harry's posts are going on about, all odd.

 

[RandomGrinch]

...And before getting too carried away, consider the ceiling height. The critical measurement as far as building regs are concerned is 2m height (although reducible to 1.9m at a push) at the top of the stairway. Your new floor joists may need to be of an appropriate size and material to achieve this.

Although a little dated, I've found this guide helpful to gather my thoughts.

 

[Harry Bloomfield]

Though they're not mandatory. It should be said I'm not sure what Wayner's last post or Harry's posts are going on about, all odd.

I was simply pointing out, that the red timbers in the OP's diagram would serve little purpose - they would be supporting the roof, via the loft floor/ceiling timbers, and the roof was not in need of additional support. Rather, the loft floor would be in need of additional support, if the OP was considering adding any weight to it. His red marked items, would thus be under tension.

I certainly was not suggesting it as a way for the OP, to turn his loft, into a habitable space, which later seems to have been the basic idea.

 

[Murdochcat]

Though they're not mandatory.

But proceed without one and your neighbours could get a court to stop any building work