Any builders? - Cutting out rafters?

JustOne

JustOne

Ryder Cup Winner
Joined
Apr 6, 2009
Messages
14,803
www.justoneuk.com
This is a pic from above showing 6 rafters supported on the left by the external wall and on the right by an internal one.... can I cut through rafters C & D to create a loft hatch as per the 2nd pic?

Pic 1

roof.jpg

Pic 2

roof2.jpg

I was going to add the new pieces with hangers and connect them to the sawn ends, also double-up rafters B and E.......... crap idea? Need access to the loft and sideways (between rafters) doesn't work :angry:
 
Wow, I work in the trade but im no engineer however I can say that a cut like that MAY have an affect in your roof strength.

How old is your house?
 
JustOne said:
50yrs old. The roof is supported with 2 purlins.
Click to expand...

So they wont be pre-manufactured trusses then, I wouldn't like to give you bum info but personally I wouldnt cut 2 roof joists with speaking to an engineer.

Depending on supporting walls position under these trusses there may be a potential for the ceiling to sag prior to you installing the cross timbers, you may have to support the joists to be cut underneath at each side of the cut to eliminate this whilst you create your hatch.

Like i said though im no expert and would suggest an engineer advises, you dont want your roof to come in after all.
 
I'm a roof truss designer and I can tell you

1. They are ceiling joists not rafters.
2. If you double up B and E by getting an additional timber and nailing it to the existing at 100mm centres you'll be ok.
3. Make sure you put doubled up trimmers in to support C and D.

edit:> Make sure you use C24 Timber and not C16. As it's worth paying the extra for the additional strength.
 
Last edited:
la_lucha said:
I'm a roof truss designer and I can tell you
Click to expand...

That's handy!!!!

I was going to literally TRIPLE the surrounding joists and the opening DOUBLED by drilling through and bolting with 10mm, 7 inch bolts........... it's a bit messy but basically everything in blue would be new......

[click picture to enlarge....]

roof3.jpg

Too much?
 
JustOne said:
That's handy!!!!

I was going to literally TRIPLE the surrounding joists and the opening DOUBLED by drilling through and bolting with 10mm, 7 inch bolts........... it's a bit messy but basically everything in blue would be new......

[click picture to enlarge....]



View attachment 1590

Too much?
Click to expand...

Way too much.

By Tripling the ones that are being cut, you are not adding strength but just increasing the weight to be carried.

What I said earlier is just the ticket mate. Bear in mind that these are only holding up a couple of layers of Plasterboard and plaster.

Oh and use Timberlok screws instead of bolts. Much easier.

http://www.screwfix.com/p/fastenmas...aster TimberLok Screws 6.3 x 100mm Pack of 50
 
Give me the sizes and I'll design it up for you mate. Carriage bolts are far more than is required and the Timberloks perform comparably well.
 
la_lucha said:
What I said earlier is just the ticket mate. Bear in mind that these are only holding up a couple of layers of Plasterboard and plaster.
Click to expand...

Might be a silly question but do they not play any part in roof support? Someone told me they are in tension and stop the roof from 'spreading', I thought they were literally there to hold up the ceiling and the actual roof weight is taken via the purlins and the external walls?
 
They may take some of the spreading force, but the purlins and wall plate should take most of this. It depends if the rafters are nailed to the side of the ceiling joists? They don't support the roof at all.
 
JustOne could you show us a cross section. There is a bit of confusion re rafters and joists. If, as I think, you are cutting through horizontal ceiling joists then good advice above.
You are forming quite a large opening. What is going in the opening? it could be quite heavy.
 
daymond said:
JustOne could you show us a cross section. There is a bit of confusion re rafters and joists. If, as I think, you are cutting through horizontal ceiling joists then good advice above.
You are forming quite a large opening. What is going in the opening? it could be quite heavy.
Click to expand...

The wife?
 
My tuppence worth on this is.

If in any doubt check with a structural engineer, end of, he will give you a spec to form the opening to.

The rafters are the sloping timbers in a roof and have the tiles / slates on top of them. The joists or ceiling ties are horizontal and generally support the ceiling finish and are often used to take storage, although not always designed to do this.
A 50 year old roof is "probably" over specified as they weren't trying to cut costs as much in those days. Which normally means you can do a bit more with them without fear of failure.

I would have thought that if the two full length joists which are remaining are doubled up and bolted together, then the new timbers at right angles to these can be supported off them on joist hangers, and the cut joists supported on the new bridle.

The ceiling tie of a roof truss whether it is pre manufactured or not is generally used to tie the two rafters together and stop the roof from spreading out at low level.

Whilst the joists are unlikely to fail, unless seriously overloaded with storage, water tanks etc then the worst that tends to happen is excessive deflection at the mid point.

Last minute thought, does the opening have to go that way ? If it was oriented in the other direction then it would mean cutting less ceiling ties / joists.
 
Last edited:
Just to clarify... I'm cutting out ceiling joists to make a ceiling hole into the attic large enough to fit a loft ladder, it can't fit the other way as there'd be nowhere to extend the ladder. If I only cut out one joist it still doesn't fit. The loft space/roof ISN'T built/supported with modern 'A frame' trusses. The pics in the opening post represent a part of the loft (over a bedroom) that is approx 3sq/m
 
Last edited:
You must log in or register to reply here.
Top