Fitting Loft Hatch - Need Advise On Cutting Joist!

[n-hatton]

Hi All.


Looking for advise\reassurance on job cutting a loft hatch and joist. Have good basic carpentry experience - no issue making frame and hatch etc - but no structural experience!

(I'll use this link for my reference
http://www.diydata.com/general_building/roof_construction/roof_construction.php )

House; early 1900s mid-terrace. No prefabricated roof trusses, amazingly only has rafters - and possibly purlins with ends supported in the brickwork of the two gable walls!? From memory; there may have only been one set of hanger and struts at each end of the loft - if any at all (DOH can't remember!) Loft was one amazingly large open space for such a small house - no storage tanks etc! There's a central staircase with supporting walls passing right up both stories to the loft joists at the two points in the diagram where the strut bottoms connect to the joist.

I need to chop one joist dead-centre between the supporting walls - centrally on the landing therefore. Will obviously temporarily fix two large heavy battens of timber to tie the joist I'm cutting so ends supported by the two neighbouring joists. Then cut and screw permanent end plate to support the cut ends to neighbouring joists before dropping in my own-made loft frame into the aperture. The two cut joist ends should in theory be laying on the supporting walls below.

Assume this is all sound theory? Unless of course the joist I need to chop happens to be one of the possible two with the hanger and struts attached?

The diagram, which I'm assuming maybe wrong, makes it look as if chopping a joist will cause it to cantilever "up" with the weight of the rafter being fixed on the end of the joist and out passed the wall plate? I thought the bottom of the rafters would be purely supported on the wall plate? I assume the joist does "tie" the bottom of the rafter to prevent it from splaying out and off the wall plate? Any risk as I chop!?

Assume I should not cut more than one joist?

Also, hatch will be right at top of stairs - told customer I'd be concerned for safety if stumbling off the loft ladder - then straight down the stairs! Any come-back issues\regs if customer insists on this location?

Beginning to have doubts now



Cheers,
Neil

Pic of where hatch will go - probably unhelpful
http://yellowwestie.comlu.com/avatar/Loft-HatchAdj.JPG

 

[mutantgoat]

Whatever you do DO NOT cut the purlins
ceiling joists/rafters if cut need to have trimmers across the cut ends to the other joists. 3-4 joists with trimmers is ok
If think the cut joist will cantilever up, screw a piece of 2*3 across that and the two on either side
Note that the roof space joists will need reinforcing if there is to be a usable floor. There are building regs specifications for the joist depth for the spans and loads
I'm v.worried about the loft stairs continuing directly in line with the present stairs. A fall down both could be serious , even if the client authorises it and accepts all liability, you are the expert and you've put it there. How much have you saved to spend on legals?
If this is going to be a usable room, you should also have building regs approval
I've done a few of these in terraced houses and they look great with all that uninterrupted space. For a inexpensive job on the cheap without the regs and reinforcement, I would walk away. Sorry.

 

[n-hatton]

Mutantgoat.


Thanks for your reply

Looks technically sound - the joist cutting part of the job - in normal circumstances I'd have a go. However, and on balance, everything else seems so wrong with the job. Involves a hell of a lot of work for what is normally supposed to be straight forward! No doubt the customer will not understand the cost\labour I'd have to quote for.

The landing is a tiny 700mm x 800mm step at the top of the stairs. I've got to cut an almost identical size hole in the ceiling directly above, remove and terminate existing coving, otherwise there's not enough width left for a decent sized hatch, there's no real room for architrave either - so need to consider other ways of making it all look neat, customer wants hatch to look "concealed" - and all while standing tip-toe on the top step carefully cutting lath and plaster so damage doesn't spread!

I'd need to put up a ladder and run boards out over the stairs for my own protection! Let alone, as you say, any comeback if the customer has a fall!

You're right, I'm gonna walk away.


Cheers,
Neil