loft floor joist direction

[johnwt]

my question is quite simple.

im in a mid terrace with purlins supporting the roof, 2 on each side.

why cant the new floor joists be layed from one internal wall to the other rather than installing steels just to keep them inline?


im not an engineer but the way i see it having support all the way along the floor im laying seems better than two massive steels focusing weight in one spot.

all replies welcome.

 

[freddiemercurystwin]

The steels will be required anyway to support the purlins, when the purlin struts are removed. Also there is considerably less disturbance to the party wall, as hanging the joists off them will require. What is the span between the party walls? As once you reach a certain distance an all timber solution for the floor becomes financially impracticable. It is possible to get the joists lower and run in between the existing ceiling joists but it is often a little more complicated solution, only worth doing if space is a premium. Have you asked your engineer?

 

[johnwt]

the purlins have never had any support as far as i can tell.

there are two purlins each side one about shoulder height and the other at knee level.

what i propose to do is run my new joists across the ceiling joists into the brick wall as this is 4.3m which means i could spread the load without touching the joists below.

sorry for the confusion.

 

[freddiemercurystwin]

Are you keeping the shoulder height purlins then?

 

[tony1851]

As the boss says, it is usually easier to run the floor joists front-to-back (ie parallel to the ceiling joists) rather than side to side.

If your span is only 4.3m, and assuming you are not building a dormer, you might be able to use timber main beams instead of steel.

 

[freddiemercurystwin]

As the boss says, it is usually easier to run the floor joists front-to-back (ie parallel to the ceiling joists) rather than side to side.

Did you mean perpendicular?

 

[johnwt]

Yeah going to keep the purlins where they are. Don't want to mess with them.


As its a mid-terrace the width of the house is 4.3m but the length is closer to 9m.
I'm not planning a dormer.

The main plan is to make floor sturdy enough to walk around on without impacting the ceiling below.

 

[tony1851]

As the boss says, it is usually easier to run the floor joists front-to-back (ie parallel to the ceiling joists) rather than side to side.

Did you mean perpendicular?

In a typical terrace house, don't the ceiling joists run front to back, ie in line with the rafters?

On second thoughts, maybe in London it's side to side in the older houses?

 

[johnwt]

ive been advised to set my new floor joists at 90 degrees to the exsisting ceiling joists and use wall hangers in order to suspend it above the joists below.

any thoughts?

 

[sh4tz]

ive been advised to set my new floor joists at 90 degrees to the exsisting ceiling joists and use wall hangers in order to suspend it above the joists below.

any thoughts?

I also would like to know if this is a sound idea. Similarly, my semi detached has current 4x2 joists running from back to front with the joist span only being half the length of the house as they sit on a cental dividing brick wall. I want to do same as you and fix new elevated joists, perpendicular to current joists, from wall hangers on the party wall, spanning about 4.5m and sat on a dividing internal brick wall. Therfore creating a floating floor independent of the existing joists/ceiling.

Though I can't find anything about the do and don't of putting a perpendicular joist floating floor on the Web.

As johnwt asks, any thoughts guys?

 

[tony1851]

There's nothing wrong in principle with running the new floor joists perp. to the existing ceiling joists. The main down-side is that it uses up valuable headroom - on a 4.5m span you'll need at least 200x50 joists.