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Building Q

The Captain

The Captain

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Hi chaps,

noticing some with knowledge of build work on pfm- if I could ask on here:

I have an 80's single story extension (onto my 2 story cottage), comprising of a kitchen + tiny bathroom. Pitched roof ontop. Loft between.

I have the idea of extending up, to convert the loft space above kitchen (5x5m) into a proper-sized bathroom, & landing/ stairwell above the existing tiny WC. Effectively the pitched roof goes back ontop.

What I find, poking my head thru kitchen ceiling hatch, are ceiling joists built of 3x2". This guage seems normal for ceilings, with a loft space being above, as I also find 3x2 used for another 2022 extension ceiling (loft above).

Q is.. Are 3x2 joists sufficient for the floor, for the proposed bathroom above the kitchen-?

Thanks, Capt
 
Absolutely not.
A quick look at the timber span tables suggests 220 x 63 mm at max 450 mm centers for a 5 m span.
If you want a bath you will need more.
I highly recommend talking to a structural engineer.
The timber span tables are readily available online.
 
Alexm2033 said:
Absolutely not.
A quick look at the timber span tables suggests 220 x 63 mm at max 450 mm centers for a 5 m span.
If you want a bath you will need more.
I highly recommend talking to a structural engineer.
The timber span tables are readily available online.
Click to expand...

Ah thanks Alexm,

I hadn't heard of timber span tables so didn't know existed online.

I'm not imminently doing said build myself don't fret! I realise whoever builds it, it'll need to pas Building Regs. Likely a pro doing outer xyz (including a new floor then, sigh/ adds a £chunk you see) then myself building inner xyz as with my '21 extension, which passed B.Regs.

Thanks, Capt
 
Rule of thumb used to be joist depth in inches needed to be half the span in feet for 2" sawn at 17" centres iirc.

Probably inadequate for current regs but my bath hasn't fallen into the kitchen yet.
 
.. just close-up the centres of the joists under the bath to maybe 300mm, if worried - but even as originally suggested, it'll be fine.
UK typical domestic floor live loads allowances are 1.5Kn/sq.m; a bath, silly-full, is going to be under 300Kg, floor deck spreads that over >2sq.m anyway = no problem, well within factor of safety implicit in the tables/ their calculation.

(in fact typical 1550mm long bath with 200mm of water in it before getting -in - is only about 100Kg of water.)
 
Don't worry about the bath, you don't need any extra joists as long as you get them right in the first place. i'd be looking at posi-joists so you can run plumbing more easily etc. They are better for wider spans too.

However, something you will need to check first is that the footings for your single storey building are deep and substantial enough to support a second storey. This will require a dig down next to one of the walls if you don't have the original plans and building sign off to say they were built as per the plans.

Edit: Metlor posted at the same time
 
Thank y'all.

Foundations.. of course, I hadn't thought of this: the existing 80's single story extention is generally pretty bloody average quality at best: I know of a grand total of 1" of wall PIR used! Meaning kitchen & bathroom as they are, are FKN FREEZING in winter (afaict no PIR whatsoever below kitchen floor too).

Hence one reason for needing a proper, warm bathroom. I cannot use shower in autumn/ winter/ spring, as it's so unpleasantly cold in this teeny ground floor bathroom.

Urgh foundations.. I've a bad feeling it is minimal, like the wall insulation situation.

Thanks great help chaps. Capt
 
Thinking further..

my recent build 2-story extention (t'other end of cottage) is timber frame, each of the 3 wall sections hauled into place/ plonked onto the 1st floor joists (iirc). The outer course I chose block, & render to finish.

IE surely if I did the same & went timber frame again -my intention as cheapest construction method- plus then adding timber 'cladding' for my outer course, being both the cheapest & lightest 2nd course.. my likely minimal foundations I have, might be just sufficient to accommodate such a 'reasonably light' additional load.

Capt
 
Might well be, and that would be my recommended approach - talk to whoever you used for founds & sim, for this last recent work.
 
The Captain said:
Thinking further..

my recent build 2-story extention (t'other end of cottage) is timber frame, each of the 3 wall sections hauled into place/ plonked onto the 1st floor joists (iirc). The outer course I chose block, & render to finish.

IE surely if I did the same & went timber frame again -my intention as cheapest construction method- plus then adding timber 'cladding' for my outer course, being both the cheapest & lightest 2nd course.. my likely minimal foundations I have, might be just sufficient to accommodate such a 'reasonably light' additional load.

Capt
Click to expand...
Like Martin this would be my approach, but I'd dig down and find out what footings you have anyway... to be honest a lot of single storey builds have footings for double storey construction as most of the time builders in the 70s and 80s just did standard 'house' footings regardless. Timber framing the top half is a good approach as it's easier to build and you can get better insulation levels too. Just be sure to cost up your cladding as this can be expensive... some really good composite options available now so no maintenance and much nicer looking than uPVC.
 
martin clark said:
Might well be, and that would be my recommended approach - talk to whoever you used for founds & sim, for this last recent work.
Click to expand...
Hi Martin, good advice thanks for your input.

Actually I prolly wouldn't have needed this thread, if I could've got my builder here for his expert thoughts (he'd have been choice 1 to do the outer work), as he built me a splendid extension on t'other end in '21. A pillar of our village. But would you believe it, he was diagnosed with MND December '22.. & died in August (69). Huge shock for our village & community. I used to stand next to him in our tiny welsh church, lovely man he was. RIP Dai Neil Davies, a friend.

Anyway I have a 1m concrete 'path' in the way preventing doing a test dig, which surrounds the 80's kitchen extension. So I'd need to I dunno, jack hammer a section of it clear, to then dig down.. summink like so I guess.

Thanks, Capt
 
Before you do any digging juts check your local authority planning department to see if they have any records of when it was built. In the 1980s they started keeping better records of planing applications and building control documents so you may strike it lucky and be able to see how the extension was constructed. You will probably need ground samples doing anyway - any surveyor can do this - they just drill a hole down to the footings level and take a ground core sample which is then analysed for suitability for bearing additional load. Should be fine as your house is already built, but planning/building control will doubtless want to check.
 
WYAIT would it be worth sorting out the insulation downstairs?

Maybe exterior clad in same finish as the new bit.

Max bath weight could be over 400kg with Mr & Mrs Archimedes but my old architect said that a properly built floor is stiff enough to take a baby grand.
 
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