Installing a loft floor

Yes John - it may potentially be that 2 x 6 joists (which are significantly cheaper per metre) could do an adequate job in this application, if they are available (my local timber yard couldn't supply that length for the living room when I was costing it: There, the lower spec was due to the wall running along the middle, effectively halving the span).

TBH, I didn't spot Tony's software - I thought he just mentioned the rule of thumb(!). If I did go below spec (say 4m of 2 x 6), it would be great to have some idea of how wobbly such a floor would be. The joist tables just give maximum length for size, as far as I can see.

I'd still feel a little uncomfortable that it would deny the option of making the space habitable in the future though, even though the rest of the house is big enough that it shouldn't be an issue. Although I get the point that BR specs change over time, they surely can't ask for joist that are much deeper than they require now, so I would have thought the current specs won't change much.

(Apologies if my posts are hard to read. Someone told me a while ago they weren't wrapping, whilst in a recent thread someone else told me they had a lot of empty lines!)

cheaper per metre) could do an

couldn't supply that length

the wall running along the

A timber merchant ought to be able to get 6x2 in 5.3m lengths at least.

thumb(!). If I did go below

a floor would be. The

I just checked, there is still a demo available. It has printing knobbled - but that won't be a handicap for your needs.

It will show you the calculated deflection for whatever load you apply, and also tell you when you are exceeding the safe working limits on the timber.

If you model your longest timber that should let you get a feel for the changes. The loadings to apply for a normal floor appear further up the thread (if you know what you are storing etc you may be able to use lower figures)

the space habitable in the

shouldn't be an issue.

Might be worth working out what you could "get away with" and then comparing the cost difference to doing it to full spec.

for joist that are much

change much.

I would not expect them to change in substance at all really. They may grow to include more on composite joists (i.e. man made beams with struts top and bottom and some sheet material webbing)

weren't wrapping, whilst in

Its a combination of not wrapping and all the lines being double spaced. The former is easy to fix in a reply with a quick CTRL + R in thunderbird. That latter takes slightly more editing!

That's exactly the point. All Victorian loft floor joists were compliant for habitable use at time of building, but no BCO is going to accept them in a conversion today.

NT

cheaper per metre) could do an

yard couldn't supply that length

to the wall running along the

thumb(!). If I did go below

such a floor would be. The

making the space habitable in the

shouldn't be an issue.

ask for joist that are much

won't change much.

weren't wrapping, whilst in

Thanks for the link - Now I have to find a Windows PC I can spark up and run the software - should be interesting.

I suspect a narrower joist could be significantly cheaper for these timbers, although it might not make a substantial impact on the job cost overall. I've rather taken a 'do it properly and do it once' approach to this house, rather than being cost-driven.

I did toy at one stage with the prospects for making up composite joists in situ, given the access issues, but decided that would just add another variable (and potential disaster) to the equation (!)

Must have another go at Thunderbird for this group. I had it working, then it wouldn't post for some reason.

I don't quite follow the line of thought. A loft floor in 1924 was *not* designed for habitable use then, so its no surprise it would not be considered adequate now.

Your point seems to be that the definition of "habitable" did not exist in 1924. However to cut through the confusion, look at what would have been installed in 1924 for a normal 1st floor set of joists, since that will have been designed for what we would today call habitable. If the loft had similar spans but thinner joists, (which which is a safe bet) then its not habitable - then or now.

Probably not as "industry standard" or trustworthy, but there are a number of smart phone apps about that will do calcs at least on a single beam. Might be worth trying one of those if you have platform for that.

It depends a bit on the layout and how many joist hangers you need etc. Those will be the same price regardless.

It ought to be fairly painless for newsgroups if you are using your ISPs newsserver. If using a third party one, you may need to turn on the "request authentication" option in the account settings.

I don't think you've followed what I'm saying at all.

NT

I should take a browse through the phone apps (without wishing to turn the thread into another debate about which phone is best!) Your comments about ISP newservers made me realise that I set Thunderbird up for home, then might have failed to post over a different WiFi connection, so if this posts, problem solved (ish)

So what is your point then? I thought we had covered:

Have I missed any?

Hence why I did not mention a platform. I have seen them for mine, so I presume they exist for the others... I wonder if Tony is planning on an Android or iOS port of superbeam proper?

Normally if the newsserver accepts authentication then it will allow posts from any network. If it does not, then it will usually only accept them from its "own" network address block.

BTW the quoting looks much better - no double spaced lines anymore ;-)

No current plans. Would it be an interesting project? Probably. Would it make any money, given what people are used to paying for mobile apps? Probably not. If I was looking for an alternative platform, then the most likely route would be a web-based app, accessible via any browser.

Excellent! Problem solved then (now to work on the typos....)

One option would be to only sell/give away the mobile app as an extra for the full PC version - gives you the sales hook for some added value on the main product, stops folks who already use it going to alternative platforms since they can still use the mobile version of the "industry standard", but without cannibalising your desktop sales.

On 23/10/2012 01:43, John Rumm wrote:

are a number of smart phone apps about that will do calcs at least on a single beam. Might be worth trying one of those if you have platform for that.

It's interesting that there seem to be more apps available than web-based calculators. Unfortunately most of these seem to be in American and I'm not sure how C16 compares with their specs but, putting a trial dimension of 4m in, using Redwood or Southern Pine (which seem to come out the same and probably equate broadly) gives a deflection of

Give me the specs of a beam if you like and I will see what numbers I get...

When you add floor boards, you can use load sharing in the calcs - since you tie a number of them together in effect, the statistical variation is likely to reduce, so you can assume stiffness's no so close to worst case.

Well indeed. Also a loft just used for storage will not be loaded to anything close to what one needs to allow for a room.

toys, old masters and all that.

unsupported 14' span of 2 x 4

they didn't bang on the

visible deflection. it helps if you bring reality into this.

sometimes noggings, both of which spread loads over multiple joists

best outcome and b) I

Perhaps 2 x 6s would do the job

(currently completely off the radar)

to lug them up 3 floors

all support a fully loaded loft without problem.

In my Victorian house I put a 4 foot fluorescent light up in my study (an ex-bedroom) and was puzzled by why the second screw wouldn't reach through the L&P ceiling to the joist. On standing back from light I realised the reason was that the ceiling had sagged and my fluorescent was bridging an inverted hump. It's now fixed with longer screws and with the centre touching the ceiling the ends are a good inch below the ceiling - so a deflection of about 1"/2'.

-- Phil Addison

I'd put at a beam at right angles to the joists in the middle of the ceilin= g, supported by acro-props. This will halve the effective length of the jo= ists, and make them plenty man enough for the job.

You'll then need boards on top of the joists to stand on.

Sounds like a reasonable plan. I'd probably just use a rawl-plug and No 10/ No 12 screw. It doesn't have to take much weight, and it doesn't have to take it for long.

Thanks John, that would be very useful. All lengths are 4m (a little variation but no more than 100mm) and the TRADA tables say a 47 x 195 joist is good for that at 400 centres but of course give no further information. (A number of apps etc simply give the same data in their calculators - you put in the size and it tells you the max span.)

Clearly very small ones would be inadequate at this length, but it would be interesting to know what the performance of 7" (ie 47 x 170) and 6" (47 x 145) would be at 4m for C16 timber. From what the tables indicate, the advantage of C24 is pretty minimal, so hardly worth the trouble of sourcing etc except in very marginal situations).

I'll most likely cover with chipboard (8x2 t/g sheets), which comes in

It's also pretty clear that a span of 4m will benefit from strutting at mid span, so that's on the agenda too.

Friday night - must be time for a cold one (!)

Cheers!

Well if I model that with a uniformly distributed load of 0.8kN/m (long term load), and treat them as a load sharing system, you get a deflection of just under 11mm. Go down to 175mm and the deflection goes up to just under 15mm. However its worth noting that it is also flagged as failing in maximum permitted bending stress at that point. 150mm and deflection is nearly 23mm. 100mm and deflection is approaching 80mm!

That is a full floor load though - unless storing a large magazine or record collection its unlikely you would reach that.

C24 at 175 for example would be a "pass" on 175mm (deflection 7.61mm) and on 150mm (11.98). (125mm and you are back to failing in bending stress)

Note also you can push it firther with short term loads - so you don't necessarily need to make adjustments to factor in someone clod hoppering around up there shifting the boxes.

It interlocks, so only really needs enough screwing in this application to stop it sliding about.

It will make it bounce less. How much that matters for storage space is debatable.

Sounds like a good plan ;-)