Joist q for loft conversion

[Dylan T]

Hi all -

I'm currently trying to gauge feasibility of a loft conversion; it'd be something I'd consider doing myself (or at least managing it myself) and I'm particularly trying to work out the difference of what is required to convert properly to bedroom or simply use it as a second play room. I've spoken with my local council who directed me to an online document, but it really lacks any kind of technical information.

In short, the current joists span an area of 6.5m from outer wall to outer wall, with no other supporting walls. The joists are 9x5cm, and the highest point from top of joists to bottom of rafters is 222cm (and the point of entry where the door would be is around 210cm).

The rafters are also resting on 4 (2 on each side) huge supporting beams which even if I box around as neatly as possible do take up a lot of room. (They're also starting to crack as have been there for around a century i'd say). Photo here:
https://cl.ly/d0bb6fcc5265

I'd really appreciate if someone could help me with the following questions:

1) Could I remove the beams supporting the rafters in favour for vertical supports on each rafter? (like here https://cl.ly/931a3399457c)
2) I am assuming I'd need to replace the joists, but does anyone know the thickness I'd need? I read somewhere about a type of timber which is extra strong and therefore isn't required to be as tall, thus saving space, but I can't find the page. I can't find any calculations on this online or in the council docs.
3) As there are no supporting walls, are the joists brought in through the roof or is there a fancy way of using a join or even steels with some sort of connecting flange.
4) Is there a way of adding a supporting beam midway to supplement the lack of a supporting wall and therefore require smaller joist beams?

Thank you everyone so much!

 

[FRAN1870]

Hi all -

I'm currently trying to gauge feasibility of a loft conversion; it'd be something I'd consider doing myself (or at least managing it myself) and I'm particularly trying to work out the difference of what is required to convert properly to bedroom or simply use it as a second play room. I've spoken with my local council who directed me to an online document, but it really lacks any kind of technical information.

In short, the current joists span an area of 6.5m from outer wall to outer wall, with no other supporting walls. The joists are 9x5cm, and the highest point from top of joists to bottom of rafters is 222cm (and the point of entry where the door would be is around 210cm).

The rafters are also resting on 4 (2 on each side) huge supporting beams which even if I box around as neatly as possible do take up a lot of room. (They're also starting to crack as have been there for around a century i'd say). Photo here:
https://cl.ly/d0bb6fcc5265

I'd really appreciate if someone could help me with the following questions:

1) Could I remove the beams supporting the rafters in favour for vertical supports on each rafter? (like here https://cl.ly/931a3399457c)
2) I am assuming I'd need to replace the joists, but does anyone know the thickness I'd need? I read somewhere about a type of timber which is extra strong and therefore isn't required to be as tall, thus saving space, but I can't find the page. I can't find any calculations on this online or in the council docs.
3) As there are no supporting walls, are the joists brought in through the roof or is there a fancy way of using a join or even steels with some sort of connecting flange.
4) Is there a way of adding a supporting beam midway to supplement the lack of a supporting wall and therefore require smaller joist beams?

Thank you everyone so much!

Those big beams are called purlins .... they support the rafters and stop the roof sagging.
You should consult a professional to make the required calcs but in short you won't have the height to span 6.5m because the required joist depth for that wouldn't leave you with enough head height.
Standard way is to put RSJ's from gable wall to gable wall and sling a floor from there. You'll probably get 3m as your height looks very similar to mine.
The RSJ's will allow you to build up that vertical wall upto a strongback then take out the purlins (although when I did mine I left them in and made a feature of them).

You can't support the purlins from the rafters

You will also need to have enough insulation to meet building control so you lose head height there.

 

[geraldthehamster]

What do you mean by "span an area of 6.5m from outer wall to outer wall, with no other supporting walls. The joists are 9x5cm". Are you saying you have 3 1/2" x 2" joists spanning a length of 6.5m with no additional support?

There is no difference in building regulations terms whether you intend to use the room as a bedroom or as a playroom. A loft conversion is a loft conversion. The same regulations for flor, insulation, stairs and fire protection apply.

 

[FRAN1870]

What do you mean by "span an area of 6.5m from outer wall to outer wall, with no other supporting walls. The joists are 9x5cm". Are you saying you have 3 1/2" x 2" joists spanning a length of 6.5m with no additional support?

There is no difference in building regulations terms whether you intend to use the room as a bedroom or as a playroom. A loft conversion is a loft conversion. The same regulations for flor, insulation, stairs and fire protection apply.

Those joists ceiling joists span from stud wall to stud wall. I doubt they are actually 6.5m long. Whatever happens they are only strong enough for light storage at best.

 

[Leofric]

You need to have plans and a Building Regulations application prepared and submitted for approval to Building Control who will require structural engineer's calculations for the structural alterations. You need to consider whether it is worth doing taking into account the floor space that will be available with decent headroom in the loft and taking into account the room you will lose on the first floor to incorporate a new staircase for access to the new room in the roof space. Are there also water tanks in the loft to consider. If you do decide to go ahead there are companies that specialise in loft conversions who should know the best solutions to suit your property.