truss roofs

[beaver74]

hi all

now i know that truss roofs are designed to a tight spec and as such cant be drilled
but i have come up against a truss roof that has been designed around 3 bed rooms and as such the floor is infact the ceiling of the lower floor which i need to wire but this needs the floor being drilled
has any one come across this befor
i will be getting the customer to contact the chippy but after a few options

 

[Spudnik]

Not sure i see how a truss roof can have rooms "in it"?

Do you have any pics?

 

[beaver74]

afraid not but it has been designed around the rooms

 

[DurhamSparky]

i got a quote to convert my loft!!!! truss and all ....

£35k

in the wrong job!!! they wanted 4k just for electrical work! apparently its all Part P and Building control registered!!

 

[nickblake]

So you trusses what thickness are they you should have say a 75mm x 50mm 2 sides (rafters )and an 200mm plus as the bottom ( joists) so forming the floor the main rafters you shouldnt need to drill because you should be able to go between and run the cables either side or the ceiling voide difficult to describe without the picky

for drilling you should be 50mm from top or bottom max diameter of the hole should be 0.25mm x joist depth holes in center line between 0.25 and 0.40 x span max depth of a notch should be 0.125 x joist depth notches on the on top in a zone between 0.07 and 0.25 x span and holes should be at least 3 diameters apart

hope thats of help if ive understood the question

 

[nickblake]

4k to wire you loft i get moaned at for £3k to wire a 4 bed house Should we be impressed that it would be Part P ,tell em youll do the leckys bet youd do a way better job

 

[Phil]

4K does he want a subby??

 

[netblindpaul]

IF the beam is symmetrical, you drill at the exact centre line of the loaded beam, and, the hole you generate has sufficient radius such that it does not act as a stress raiser, then it may be possible to drill the structural joists.
Remember that a structural joist IF symmetrical has no loads along the neutral axis (NA) compressive or tensile, thus why it is permissible to drill at the mid point as this is “normally” the NA.
This is structural engineering theory, beam design calculations were part of my degree course.
Paul

 

[DurhamSparky]

4k to wire you loft i get moaned at for £3k to wire a 4 bed house Should we be impressed that it would be Part P ,tell em youll do the leckys bet youd do a way better job

i laughed at there quote!

i was not a "part p" spark when he quoted so could not really input the i will do it my self card as he would only throw the build regs at me..! but i would just use building control to sign off for £130 quid..! i win each time!!

i just nodded at the bloke when he was talking, i only wanted a "Price" but at £35k i would happily move from my 3 bed semi to a nice 4-5 bed detached and use the £35k there considering i was loosing a bedroom to gain a bedroom! Logic!! none what so ever!

think cost of en suite plumbing was 2k , steel supports were like 4k loads of other daft money (jobs for boys) and only thing that was sensibly priced was velux windows at £340 each fitted

he asked if i wanted to go ahead any time soon..!
i said yeah i do when i find £35k down back of sofa! i was expecting like 15-18k??

 

[Yooj]

4K does he want a subby??

Probably...but the builder would still only want to pay you £5 a day, and plead poverty when you put in a fair price for the job.



Always been told that drilling through trusses was a major no-no, and seen a couple of times where a contractor had done that, and had to put right at their own expense.

However, from what you are saying, is that the trussed roof has rooms, and as such it is likely that the ceiling joists, are now likely to be floor joists, i.e. a lot beefier, and will likely be able to be drilled...however, as you have indicated, I would certainly get confirmation from the chippy, and probably the structural engineer as well as to whether you can drill the joists.

Yooj

 

[Yooj]

i laughed at there quote!

i was not a "part p" spark when he quoted so could not really input the i will do it my self card as he would only throw the build regs at me..! but i would just use building control to sign off for £130 quid..! i win each time!!

i just nodded at the bloke when he was talking, i only wanted a "Price" but at £35k i would happily move from my 3 bed semi to a nice 4-5 bed detached and use the £35k there considering i was loosing a bedroom to gain a bedroom! Logic!! none what so ever!

think cost of en suite plumbing was 2k , steel supports were like 4k loads of other daft money (jobs for boys) and only thing that was sensibly priced was velux windows at £340 each fitted

he asked if i wanted to go ahead any time soon..!
i said yeah i do when i find £35k down back of sofa! i was expecting like 15-18k??

You are better off getting a quote for just the structural work, and then you can do all the internals yourself. Probably only talking about £10K.

Yooj

 

[DurhamSparky]

rather just move to bigger house in nicer area!

 

[Jason Smith]

Ah, heres a question, I have a need to Notch the underside of a joist. Well aware obviously of the regs for all the other places we can invade a joist, however there is never a mention in anydocs about the underside of a joist, any one know if I can do it, and would the distances apply etc, as they would on the top side of a joist ? also,hole size etc is given in the regs in relation to the joist, and depth of notches, however there is no guidance on LENGTH of notches- on many occasions it would be so helpfull to extend the plumbers work !

 

[emjay125]

Notching the underside of a joist effectively reduces the depth of the joist by the depth of the notch, PLUS a further reduction for a stress concentration factor. Unless you are sure (and justifiably sure as well) don't.

 

[telectrix]

house has probably collapsed by now. the thread is over 3 years old.