Mains, PSUs and other goodies.

[irving2008]

@Irving: The best way I can answer that is "no idea". I'm in the end-terrace for a row that go back about 100-odd years. I suspect they were built with the attics as habitable by design. Ours has actual stairs that look like they were meant to be there, and I note that all the other houses left from this row also have dormer windows - though ours were replaced with a bigger dormer at some point.



...

Nice bench and a period chair too ;)

You should lift a floorboard or two and check the joist dimensions before you load the floor too much. A typical 100y old house would use 4x2 joists in the attic (my son's from 1903 does), they were never designed as habitable space but for light storage, tho it could be used for 'servants quarters' in larger houses, but the loading assumed very light (no heavy wardrobes etc.). Building regs differentiate between ceiling joists and floor joists. A 4 x 2 ceiling joist at 16" centres spanning a maximum of 8' (the width of a small room below) will support a dead load of no more than 500N/sq metre, an imposed (i.e variable) load not exceeding 250N/sq m and a concentrated temporary load not exceeding 900N. I'd hazard that you sitting at your substantial workbench is close to exceeding that.

Building regs do not allow for more than 1250N/sq m loading, above this they need structural design/calculations agreed by building control - this is why you need building control approval for loft conversions, especially where there is a wet room or bath installation (a full bath of water with a typical male in it is close to 2500N/sq m loading).

Again, don't want to be a spoilsport... but you don't know how the timber has faired over the years and it would be unfortunate for your new CNC build to end up in a crumpled heap on the floor below!

[JAZZCNC]

Ye what Irving said.!!. . . And if you miss align the ball-screws it will shake the tiles off your roof has well. .

[Rogue]

Ye what Irving said.!!. . . And if you miss align the ball-screws it will shake the tiles off your roof has well. .

The wind does that already...

[Rogue]

Nice bench and a period chair too ;)

If by period you mean "absolute pain in the neck for most uses" then yes. There's a stool around there somewhere that I use, but occasionally the lower seat lets me get adopt a more stable position leaning on my elbows, holding whatever I'm working on right up to the face.

You should lift a floorboard or two and check the joist dimensions before you load the floor too much.

More things to check! And lifting floorboards? I think I'd rather play with the mains again, there's less chance of getting into trouble

For various reasons we've got to have some work done on one of the ceilings underneath so we'll probably have to cut away a square of the plasterboard. I assume we can get a look from underneath. Either that or I'll definately have to wait until the kids are at school and the wife is at work!

...scary numbers etc etc... Again, don't want to be a spoilsport... but you don't know how the timber has faired over the years and it would be unfortunate for your new CNC build to end up in a crumpled heap on the floor below!

Nope, don't worry, I entirely appreciate the points you are making. Is it my first choice of location? No. Is it my only current realistic option for location? Yes. Adopt the guest bedroom? Take garden space to build a shed? The last time I successfully convinced my wife to do anything was when I asked her to marry me and, looking back, I'm starting to wonder if I convinced her to say "yes" or if she tricked me into asking in the first place. While I love her dearly, my jedi mindtricks don't work on her.

I assume that if the joists are too small there's nothing I can realistically do, short of miniaturising the build or rebuilding the attic?

[irving2008]

...stuff...

I assume that if the joists are too small there's nothing I can realistically do, short of miniaturising the build or rebuilding the attic?

Not at all, theres a few things you can do, sadly none of them very easy. The absolute simplest solution is to increase the size of the joists by bolting another alongside it. This is what you do in bathrooms under the bath. Its not ideal as a 4 x 4 still doesnt have the resistance to bending that a 10 x 2 does. Another, better, option is to add a second joist on top of the first a 4 x 2 on top of a 4 x 2 will make a huge improvement, however it does mean that you'll have a step up into the room, headroom is reduced and inward opening doors have a bit of an issue - but this is whats often done for loft conversions.

Another, more expensive option, is to bolt some steel angle alongside the joist. Obviously this has better bending resistance than wood so can use a much smaller cross-section, but it weighs more so some calcs need to be done about the overall floor weight and wall strength.

[Jonathan]

I notice irving's specified the loads in Newtons per square meter, so surely if you can spread the load by placing the benches on their own 'joists' running perpendicular to the existing joists the area and therefore number of Newtons supported is increased, perhaps enough? You'll probably be tripping over them all the time though...

[Rogue]

Another, better, option is to add a second joist on top of the first a 4 x 2 on top of a 4 x 2 will make a huge improvement, however it does mean that you'll have a step up into the room, headroom is reduced and inward opening doors have a bit of an issue - but this is whats often done for loft conversions.

...surely if you can spread the load by placing the benches on their own 'joists' running perpendicular to the existing joists the area...

They say that great minds think alike, but then again they also say that fools seldom differ. This is the first thing that occured to me when I read the post. Can the joist be on top of the floorboards? Basically creating a raised platform at one end of the room? Hopefully Jonathan and I have great minds but I must admit I'm not doing our side any justice at the moment.

Edited to add: Ahh, I guess you mean the extra joist being lined up exactly on top of the old joist, not perpendicular to it? Still, same question applies!

[irving2008]

They say that great minds think alike, but then again they also say that fools seldom differ. This is the first thing that occured to me when I read the post. Can the joist be on top of the floorboards? Basically creating a raised platform at one end of the room? Hopefully Jonathan and I have great minds but I must admit I'm not doing our side any justice at the moment.

Yes in theory, but you'll need to support the joist at the wall at each end using joist hangers and not just terminate it at the wall. Although just having an additional joist on the floorboard will improve the 'bending' aspect by spreading the load, it wont reduce (indeed it will increase) the shear force at the wall and the underlying joist could still fail with the load. The correct solution is to lift the floorboards, add new joists, cutting them back into the wall and then board over with 18mm OSB which will be a lot stronger than the old floor boards. The new joists need to be securely attached to the old ones at no more than 600mm intervals, either drilled and screwed through into the old ones (BIG screws lol) or you can use retaining straps screwed to lower joist and taken over top joist in a notch and back down to lower joist, tensioned, and screwed through into both joists. Tensioning the straps needs some sort of tool...

Incidentally the minimum joist size now acceptable for loft conversions and new builds is 9 x 2 but 10 x 2 is usual as this matches the 10"/250mm insulation depth requirement and allows direct boarding over.

[Rogue]

Yes in theory, but you'll need to support the joist at the wall at each end using joist hangers and not just terminate it at the wall. Although just having an additional joist on the floorboard will improve the 'bending' aspect by spreading the load, it wont reduce (indeed it will increase) the shear force at the wall and the underlying joist could still fail with the load.

Which realistically means "no" in this scenario. Fair enough.

The correct solution...

...sounds painfully expensive and simply not possible at this moment in time, certainly. Hmm.

Incidentally the minimum joist size now acceptable for loft conversions and new builds is 9 x 2 but 10 x 2 is usual as this matches the 10"/250mm insulation depth requirement and allows direct boarding over.

I think the first step will to be to work out the joist size and then plan around that in terms of what can be safely done. That might scupper things more than anything else.

[Rogue]

I'd hazard that you sitting at your substantial workbench is close to exceeding that.

Ahh yeah, forgot to mention. I suppose this won't be helping either?




Except now it's got a 2m long double layer of MDF (that was only a temp worktop for the picture) and a pillar drill on it...