Fixing battens to joists

[Flotsam1664]

Hi all,

Pretty straight forward question. I'm looking to fix some 2x4 (95mm x 45mm) battens perpendicular to the joists in my loft in preparation for laying another 100mm of insulation between them, on top of which I want to board an area approx 2m x 3m for storage.

What's the best way to actually fix the 2x4 to the existing joists (the height being 4 inches obviously, rather than 2)? I wasn't sure whether using "L" brackets on the intersections would be preferable to screwing the timber together. In the case of screwing, what length screws and is it better to screw in from the side at an angle or countersink straight through the top?

Thanks in advance.
Flotsam

 

[PrenticeBoyofDerry]

I would go in at angle from both sides, 60mm screws should be fine.
Normally best to plan from loft hatch and be careful not to damage any electrical cable and also power circuits require to be able to dissipate heat, so if you do have any circuits for sockets, showers, cookers etc.. running through loft they do not want encasing in thermal insulation. Lighting circuits on 5-6 Amps are generally okay.

 

[Flotsam1664]

Many thanks for the info.

I need to get up there this weekend to have a proper root around to see what's what, but will make sure I clock all the electrics whilst at it.

Main issues I foresee are three spotlights in the ceiling below, around which there is no insulation currently (I read that upturned terracotta pots might come in useful here to maintain distance between the spots and the insulation) and an old metal water tank that I think might just have to stay up there for now as I don't have the tools - or the will - to cut it into bits to bring down.

Cheers
-Flotsam

 

[PrenticeBoyofDerry]

There are a number of protective measure regarding downlights, you can purchase such as the loft brace
http://www.tlc-direct.co.uk/Products/JC94020.html
Or you could construct something similar, what you need to remember you are trying to give the lamp an area of ventilation were heat can safely dissipate to.
Also if the lights are supplied via transformers, they also require accessibility and ventilation.
With regards to cold water storage cistern, you could always put a layer of insulation within it, to help with prevention of heat loss.

 

[tony1851]

As regards fixing the joists down; personally, I would have screwed from the top down, rather than sideways at an angle as top down would be more positive.

The downside is that you would have to counter bore (say 25mm holes?) about half-way down to get 4" screws in.
Just an opinion.

 

[b21playa]

I'd go with what tony1851 has suggested. Use a flat wood bit to make the initial hole. Put some insulation/masking tape on the bit to use as a depth guage

 

[Flotsam1664]

Sorry for the delay in acknowledging the very useful advice on here, but it's only now that I've got around to starting the job.

I decided to bore down 45 mm or so down into the 2x4 and use 100mm screws to attach them to the joists. I was worried that I'd end up splitting the wood going in at an angle at the bottom. I've seen our chippie doing it without problem when doing stud work but seemed like a safer option for a relative novice like me.

In any case, what I've done so far I'm pleased with, and taking into account PrenticeBoyofDerry's comments I'm planning on getting some of the Loft Braces or Downlight Covers from www.tlc-direct.co.uk for the spots, and have taken up what little electric cabling there was to now lie on top of the insulation surrounding the boarded area.

I honestly don't know if the lighting circuit is 5-6 amp, or indeed if there are other kinds; it's pretty old red/black wiring that was already under 100mm of insulation and passes under the trusses etc so would need a sparky to get it up and re-wire. Is it generally ok for lighting circuit wiring to be underneath the insulation?

Cheers
-Flotsam

 

[IJWS15]

I know assumptions are dangerous but if I was doing it and the cables were under the existing insulation then I would assume that they had been rated for installation under the installation and leave them where they were.

You should leave an air gap between the insulation and your boarding, 95mm battens and 100mm of insulation indicate no air gap.

 

[Flotsam1664]

Just to put the finishing touch to this, the work went as planned as mentioned above. Witches hats (!) on order to cover the spots, and all insulation and boarding complete aside from that.

IJWS15 good point about the air gap, I had read it was important and was a bit concerned about it until I laid the insulation and to be honest I reckon that there's enough clearance under the boards, despite the insulation supposedly being 100mm. Seemed to be more like 90mm once it had time to settle.

Thanks again all. Happy with the job, and did it for about 1/2 the cost of quotes I was getting for simply throwing down some insulation over what was there already.

Cheers
- Flotsam

 

[PrenticeBoyofDerry]

So missed your updates on the project.
The best way to find out the fuse size protecting the circuit, would be to go to the fuse board/consumer unit and hopefully board is marked up to identify the circuit, removing the fuse or tripping the breaker dolly switch, should confirm that the device is indeed protecting the lights. In domestics, they are generally 5A (old rewirable/cartridge style) 6A (MCB with dolly switch)
The rating should be printed on the device.
It is not unheard of though for lighting circuits to be protected by higher rated devices though 10A or 16A, this would much depend on the design and load of the circuit.
The issue here would be the cable sizing with regards to routing within thermal insulation and calculating this factor to the cable size and device size required to meet the demand of the load.
When cables are routed within thermal insulation, it is not unusual for a 50% de-rating to used.
This where it then becomes important with regards to the cable sizing and protective device size.

For example a circuit with a rating of 6A with that device protecting a cable sized at 1.00mm t&e, this cable can safely carry 16A maximum.
The 50% factor then reduces the safe current carrying capacity to 8A , so you have a protective device that can only offer a load of 6A to a 8A rated cable. So this fine as the device should blow under faulty or overload conditions, before the cable melts and possibly set on fire!
But say you had a similar set up and instead of 6A device, there was either a 10A or 16A one protecting the cable, the current carry capacity of the cable is lower (at 8A) than the device protecting it, then you could possibly have a dangerous situation.
This could be resolved by increasing the cables sizing or removing the de-rating factor (bring the cable out of the thermal insulation)

Sorry if a little long winded, but hope it offers an insight to the issue with regards to cables within insulation. Lighting circuits on 5A/6A are generally okay, but other power circuits such as showers, sockets, cookers, heaters etc.. need to be looked at, as they are often already rated very close to the cables capacity before any de-rating factors have been applied.

Anyway it seems now you have completed your project, I hope the info/advice I offered and other contributions, helped you complete the project in safe way and you are happy with the results.
May I offer you my best wishes for 2014 and beyond.