Calculations for floor joists (please help)

[chebs100]

Hi there, I hope somebody out there will be able to help this damsel in distress.

My ex (a builder) started building a 2nd storey extension to our home, but stopped work on it 2 years ago, he then left in August this year, leaving the project unfinished.
I am now left with an unfinished job, thousands of pounds worth of work left to do and sorting out the mess he left us in.

The planning department recently contacted me and wanted to know at what stage I am at, so that they can do the final inspection
and sign the job off.
The building regs inspector then came and picked up on loads of things that don't comply and the costs are spiralling into their thousands, to get everything done correctly and put right.

One of the things he noticed was that lots of holes had been drilled through the floor joists for cabling and pipes, and said that because of the spacing and distance from the wall, it didn't comply.
However, he was very sympathetic and said he would pass it, as long as I could provide some span calculations, he could then decide if it is structurally sound (which he said it undoubtably is).

He said a structural engineer or a competent builder would be able to do this for me, if I sent a photo and the dimensions. Obviously with costs mounting due to all the other things that don't comply, I can't afford a structural engineer or builder to do it.

Is there anybody out there who would be able to do the calculations for me?

Here are the stats:

The span is 3620mm wide.
The joists are 190mm x 70mm.
The spaces between the joists are between 270mm and 320mm apart.

I have provided a photo.
Please let me know if you require anything further.

I would be eternally grateful to anyone who can help

Many, many thanks,
Debbie.

Untitled

• chebs100
• 22 Nov 2010
• 2

 

[DevilDamo]

I'd be VERY surprised if anybody, let alone them being on here being able to produce such calculations free of charge. The costs in having an engineer produce such calculations would be minimal to the works required if you couldn't prove the existing works were structurally sound.

 

[freddiemercurystwin]

The trouble is Building Control will be looking for professional confirmation from someone who is able/prepared to cover it with their insurance and nobody will do that for free, I don't know why he suggested a builder do it as they're not qualified to do it anyway. Sure, anyone can say it looks OK but as to putting it in writing, i think you'll have to stump up some cash.

 

[chebs100]

The inspector didn't seem too fussed about who did it.

He even wrote down some formula for me to work it out myself, but it was completely over my head. He then suggested that if I am on speaking terms with my ex, just ask him to work them out for me.
Unfortunately, he isn't prepared to do this.

The inspector didn't want it certifying or anything like that, just some calculations, so that he could decide whether it was structurally sound or not.

 

[freddiemercurystwin]

Hmm, you could try PMing //www.diynot.com/network/Static or //www.diynot.com/network/RonnyRaygun and asking them to do it, I'm sure they'll apreciate it!

 

[Static]

Well, for the size of joist 70x190 at approximately 400mm centres and standard domestic loading your spans are well within the allowable limits.. this is assuming you are boarding the flooring and securing the boards down..

What the building inspector may be looking for is someone else to take the insurance responsibility for the design which is normally a structural engineer..
But as they also mention a builder this may not be the case.. sounds like you have a reasonable inspector as some can be very demanding..

Urm.. i would think that a competent builder can look up the joists in a load/span table and provide the building control people with a short statement, if you are getting one to do the other fixes this may be the cheapest option.. hiring a structural engineer may involve a site visit and cost you £200+ just for a 2 line statement..

Static
(not so active on the forums as workload is just crazy at the mo)

 

[DevilDamo]

What the building inspector may be looking for is someone else to take the insurance responsibility for the design which is normally a structural engineer..

Well... the BCO wants somebody to prove the holes cut into the joists have not affected the strength of the joists... not if the joists are capable of spanning the distance and taking the necessary loadings because like you say, that information can be extracted from Trada's span tables.

 

[Static]

Ah i see the joist hanger now.. hmm i would be suprised if your average builder could provide a calc then.. teach me for not looking at the photo..

Anyways then the guy is prob refering to this from the BS:

"The effect of holes need not be calculated where circular holes with diameters not exceeding 25 % of the width of the member
are positioned on the neutral axis at between 25 % and 40 % of the actual length from the end or from a support."

If thats the case then you may need an SE to get it past the building inspector.. and i take back the comment about him being reasonable.. may not need an inspection of you can provide dimensions for hole locations/sizes and loadings.. etc

 

[chebs100]

Thanks, yes he mentioned them being so close to the wall.

Looks like I need to contact a SE after all then. I suppose I could draw a diagram and put in all the dimensions, size of holes etc.
Loading? What would they need to know exactly?

The joists in question are below an airing cupboard and ensuite shower room. With a plasterboarded wall between.
I suppose this might complicate things?

 

[Static]

They would need to know if the joists support load bearing walls, or partitions (ie a tiled bathroom wall straight above a joist with holes in)..
If they dont know they will assume the worst and may come up with a result that doesnt work, and then you go down the whole replace joists route and ££££ later you are wishing you had given them more info..

 

[jeds]

I would clarify exactly what the inspector wants. Does he want calcs to show the joists are sized correctly or does he want calcs to show that the holes do not compromise the structural integrity of the joists. These are two very different things.

As Static says, the joists are plenty big enough for the span and if that's all he wants then it's easy. But the holes definitely do not comply and if he wants calcs to prove they are Ok then that's beyoind most builders and you will defo need a structural engineer or a competent surveyor.

 

[theoldun]

To put this is in to language that you may possibly under stand.
Span is 3620, therefore no hole should be drilled in the joist no nearer than 905mm from the supporting wall and no further than 1448 from the supporting wall. This leaves you a length of joist 543mm long either side of the span for your service holes.
Holes should be drilled centre of joist.
If joist 190mm deep no hole should be larger than 47mm.
Distance between holes. If holes are 22mm diameter distance should be 66mm centres between holes, if holes are 25mm diameter distance should be 75mm centres between holes.
One thing in your favour is that joists are over specified.
You could ask building control if he will accept a 10mm thick x70mm deep by say metre long steel plate drilled and bolted to the bottom, each side of joists below existing pipes. If not afraid it is SE route.
Best of luck.
oldun