Loft conversion / strengthening questions

Solarchaser

Hi all, I usually stick to the green forum, but in trying to find a kind of builders forum, I noted there was this one as part of MSE, so hopefully someone can help me?

I plan to do a full loft conversion,  the double plasterboard ceilings, fire doors, all of it, bit at a time, (properly and with a building warrant) and this starts with making access a bit easier, by putting in a staircase.

I started looking into it and realised actually before a staircase i need to sister the joists which are approx 1.75 x 4 at the moment.
However when looking to make a start on this I've noticed that perpendicular to my joists run 3 timbers approx 4x2 on top of the joists, (at 1/4, 1/2 and 3/4 the length of the joists) through a lot of searching, I've found these are called ceiling binders, and the fact I have 3, suggests that the loft floor /1st floor ceiling is in fact held up by the roof, rather than the roof being supported by the loft floor.
(If I've pick that up wrong, please do correct me).

Anecdotally I know a few doors down took one of these binders, the centre one, and decided it was a bother standing upright cutting into loft height, so put it on its side, and yeah a couple of years later... the ceiling sagged.

The span of the joists is a little under 7M(front of house to back) and the span of the binders is a little under 6M (side of house to side of house)

In the middle of the house is the chimney.
I know from previous work that the 1st floor of the house is supported front to back by 2x rsj's that run from front wall to chimney, and back wall to chimney,  so the chimney is load bearing.

As part of getting a side extension and a new roof a few years ago, I got the chimney knocked down to the level of the loft floor as it wasn't used.
I want to be able to remove the centre ceiling binder, but obviously I don't want sagging issues.

So what i was thinking was I could get a glulam beam to go from side wall to side wall pushed up under the existing loft floor joists, and take one part of the chimney down a foot, and so sit the glulam on top of the chimney (I guess on a pad), this would support the centre of the loft joists transferring the loft floor loads down into the side walls and chimney. And so I could sister up my joists on top of this glulam, so that the loft floor was sitting on it, rather than hanging from the roof.

Ideally I'd speak to building control, but due to covid, they aren't there, apparently dealing only with emergencies,  which is fair enough really.

I contacted a few structural engineers and only one got back to me, (id guess the rest are isolating) and he wanted £1200 without even speaking about what I wanted to do😯(everything I've read online said to expect £2-400 for calculations).

So, I wanna crack on and do it, but I don't want to be in a situation of having to undo things later on.

So I'm thinking if the span between side wall and chimney (2.8M) requires a 6x3 glulam normally, then ill put in a 10x3, so there's no chance id have to undo it.

I see different things stated about floor loads, I see this from the Scottish government saying floor loads are deemed 2kn/m

And this from a glulam manufacturer for loads against span / sizes


Which says to me that an 80/140 should be fine for my 2.8M span, and so if I go for an 80/200, then ill definitely be OK when building control inspect.

With the covid issue it looks like we are all gonna be stuck at home for a while, so I may as well make myself productive right?

Please point out the flaws in my plan, or steer me to a structural engineer that doesn't wear a mask.

Thanks for reading, sorry for the war and peace.

Doozergirl

You're going to need a structural engineer.  Certainly in England, building control are not going to take your word for it or advise on what should be there, only check that you've complied with the SE's instructions.  

If it isn't urgent and you don't want to pay £1200 (which is unreasonable) then you will
have to wait.  

In a similar position.  I'd like to move forward a bit on our self build next door but can't even ask them to connect our electricity up because it isn't deemed essential.  

Solarchaser

Thanks for the reply.
I definitely will need a structural engineer, no argument there at all.

 I'll need one not just to spec this beam, but to let me remove the various vertical and diagonal beams in the loft to make it an open space, I'm not trying to get round this, I'm simply trying to conclusively overspec this beam so that when this thing is over and I get a hopefully reasonably priced one to do the calculations,  he can simply use the beam I've fitted, and not tell me to take it back out and do something else.
And so building control can just tick that box

tonyh66

The various vertical and diagonal beams are holding your roof up, just let the SE do all the beam specs including the floor joists then you will have no problems with BC or saggy ceilings.

FreeBear

Solarchaser said:  I'll need one not just to spec this beam, but to let me remove the various vertical and diagonal beams in the loft to make it an open space,

Sounds like it might be more cost effective to take the whole roof off and have new trusses installed - Something to discuss with the SE when you can finally get one out.

Solarchaser

The various vertical (2) and diagonal (4) beams are indeed reinforcing the roof and/or loft floor that's why I wouldn't remove them without an asher wall and detailed drawings.

And while I understand the ideal to default to needing a structural engineer, I don't have one just now, I'm not removing anything structural, and am looking to add more in.

I know lots of people in my area with the same house design that have converted their lofts by simply sistering the existing joists , some 20 odd years ago, and only the guy a few doors down has seen sagging.
NONE have got building control /SE involved... infact if they had, I'd be able to take some figures from their plans.

I'm trying to do it properly which most have dismissed as extra cost for no gain, so simply telling me to get an SE doesn't help me at all... unless you are an SE that can help me now.

DevilDamo

Even if you are proposing to install a new beam (whether it's timber or steel), it is still a structural alteration and one that would need details/calculations by a structural engineer and notification to Building Control. The chimney you are talking about lowering may also pose some structural issues and may also be notifiable?

Even in the current climate, you may find an engineer that could carry out the details/calculations with the help of some measurements and photos and therefore without having to visit the property. You'd obviously make them aware of a potential future loft conversion so all that would be taken into account at the outset.

Solarchaser

Yeah I completely agree, id see it all as notifiable, what i wanted to do was hopefully use others experience of similar situations to gauge the normal size of beam, then oversize it so that when the calculations were done properly it would show the beam i have surpassed spec, so no need for alterations. 

I've contacted 5 structural engineering firms by email nearly 2 weeks ago.

Only 1 replied and he said it would be £1200 before even seeing it.

The wife today showed me pictures of a newly completed conversion around 30 houses away, identical to mine, company came in and just sistered the joists between the 1/4 and 3/4 binders and simply removed the centre binder, and the uprights and diagonals.
This seems to be what "everyone else" has done, and why do I feel the need to be difficult cutting into walls etc to add reinforcing when "no-one" else has done it.

Maybe I should just take the path of least resistance, do what "everyone else" has done and withhold the right to say "I told you so" when it sags in a few years 🤷‍♂️

tonyh66

Do you plan to ever move out of this house? Sounds like your planning to do it before getting the calculations, just because someone 30 houses away did it a particular way doesn't mean it has been done correctly. Get it designed by someone who knows what they are doing and get the paperwork to say it has been done correctly it's a lot less painful if you come to sell it.
I'm pretty sure the existing ceiling joists are not adequate to support a floor, and sistering between the 1st and 3rd binder is totally wrong, the new beams need to sit on the wall plate to transfer to load down the walls.

Solarchaser

Do I plan to move, no.
But I want it done right.
However I'm also not paying someone £1200 for a half hours worth of paperwork, on principle!

The house 30 away, hasn't done it right..... but then no-one in my area in the last 15 years has applied for a building warrant for a loft conversion, and I know of 10+ loft conversions in my area.
So no-one locally has done it right.

No of course sistering to the binders isn't right, I was explaining what the wife was saying to me that "everyone else" has done.

However you are correct,  I am going to proceed without drawings for the fact we are locked down now, and so this is the best time to do it.
I won't be touching the uprights / diagonals/ binders as I don't want to compromise the strength, I'll deal with them when I have drawings.

But it does mean I will have to notch the new joists to go around the binders, which isn't ideal either.

Again, if anyone is a structural engineer and can help, I'd be delighted to have drawings and calculations to work from, but as I've said already, email 5, only 1 replied, and he wanted £1200 which is a disgrace.

edgex

It's not just 1/2hrs paperwork!
It's the provision of properly done calculations that you can give to Building Control, that your insurers will be happy with, & that will be covered by the engineers professional indemnity insurance.