Crawl way in my loft - Advice needed

[michael]

Just wondered if someone could give me a bit of advice about putting down some board to make a crawl way through my loft.

This is an old chapel Sunday school building (1880) and the loft is in excess of 50ft long but not high enough to stand up in as it is effectively the space above the “collar rafters”

These 4 x 2 horizontal collar rafters are fixed to the face of the 4 x 2 pitched roof rafters to form a triangulation. The spacing between the collar rafters is about 340mm centres.
The loft space or roof void is therefore effectively a triangle which is just under 3ft in height at its centre diminishing to nothing over its 7ft width.

Fixed to the underside of the collar rafters is the lath & lime plaster ceiling of a 50 ft long room which was once the school hall. So when you look up at the ceiling from this room, 15ft above you, there is the flat ceiling running down the centre fixed to the underside of collar rafters (roof void above) and an adjoining pitched ceiling either side (fixed to the pitched roof rafters).

I have three questions :-

Firstly, could you advise me if it safe to put my weight on these collar rafters as they would only appear to be secured to the main roof rafters with a couple of large nails either side (original 1880 construction)
Obviously someone has been up there before because the space is fully insulated with rolls of thermal blanket between the collar/ceiling rafters not to mention cabling to lighting etc.

Secondly, if it is safe and I am able to install a board crawl way along the length of this roof space, what’s the best material to use with regard to strength, lightness and cost? Someone has suggested either cutting up ply board or using chipboard flooring sections which I think come in a standard size of about 1500mm x 600mm (t&g).

Lastly, the thermal blanket insulation is quite thick. It’s pink in colour and stands a good couple of inches proud of the collar/ceiling rafters. I’m concerned that if I lay and fix down some board, particularly 600mm wide flooring chipboard, I would have to apply pressure to squeeze the thermal blanket down between the ceiling rafters which perhaps may be too much pressure on the old lath plaster ceiling below.
Assuming I can put a crawl way in this roof void, would it be advisable to use a narrower board, remove the insulation where the board is to be laid and then lightly stuff some insulation under the board once its fixed down.

I hope accessibility is an option here. The space needs a dam good clean out from roofing debris etc and it would make an ideal service route for running TV aerial cables etc.

Thanks in advance for your advice

Mike

 

[Penners]

Since your collars are only a little more than a foot apart, then I reckon that a roughly 18in wide crawlway made of t&G floorboards screwed to the collars ought to be pretty strong. (Note that I said screwed, not nailed. Screwing is stronger, and will avoid the impact damage that nailing could have on the lath/plaster ceiling below).

I would certainly prefer to put my trust in plywood or softwood boards, rather than chipboard. And by using T&G softwood you impart additional strength to each board from the boards on each side of it.

Stagger the joins on your boards so that they don't all join on the same collar.

I obviously can't vouch for the strength of the nails holding the collars to the rafters - only you can make a judgement on that, based on the apparent thickness of the nails and the effectiveness with which they have been fixed. But a couple of decent 6" nails on each end ought to be strong enough. If in doubt, add a screw or two to reinforce each fixing.

As to squashing the insulation, on the face of it, a couple of inches of squashing doesn't sound as though you'll be putting undue strain on the ceiling below, but once again this is something that only you can decide, based on the feel of it. If you're worried, then rip off enough insulation under the area of the crawlway to avoid the problem.

 

[Flyfisher]

For such a long but cramped space a trolley might also be useful - as per The Great Escape

 

[Penners]

And stuff the spare insulation down your trouser legs. Anyone old enough to remember the Goon Show's "Leg Lag"?

 

[Andrew Bodenham]

From your very good description I don't think there will be any problem with load bearing or defelction, so long as the collars are securely nailed to the rafters.

Choice of boarding will be depend on cost, personal preference and access. Presumably there is hatch access somewhere, and the dimensions of that may well dictate the width and length of material you can get into the loft space.

I'd have no problem with chipboard, though my preference would always be for plywood. For this sort of job I'd probably cut strips off a sheet of 18mm sheathing ply, which is the cheapest ply you can get.

w.r.t squashing the insulation I doubt if it would really be problem, given that the extra load on the ceiling would be evenly applied over a large area. But you could add, say, 2"x2" packers on top of the collar rafters to avoid the problem. Though you would be reducing the already tight headroom.

Penners is spot on about the need to screw rather than nail.

 

[michael]

Yes. It also conjures up images from Ridley Scott’s film “Alien” where the captain is crawling along the ductwork tunnels unable to detect which way the beast is coming from. I find myself having to look ahead into the gloomy abyss before me whist at the same time looking over my shoulder.

But seriously it is a long stretch of void and I am a bit fearful of something going wrong once I’m up the far end. (a collar breaking for example) It’s a long way to get back and a long way down if I fall through the ceiling. I think I’ll leave it today and try and muster up the courage over the weekend to start on Monday

 

[DaveBrigg]

Is fitting a second loft hatch at the other end an option? From experience, it doesn't take much pressure to persuade an already loose ceiling to part company from the laths. Make sure there is someone below to shout at the first sign of movement (or send a small child up instead :wink: )

 

[Flyfisher]

Penners is spot on about the need to screw rather than nail.

That'll be where the Leg Lag comes in handy then :shock:

 

[michael]

Thanks all for your advice.

If I were to cut up 18mm ply into strips rather than using softwood t&g floorboards, I presume that I would have to stagger the strips in a similar fashion to the floorboards to avoid too many fixings in any one collar?
I’m presuming the ply comes in 6ft x 4ft sheets so to achieve say a 2ft wide crawl way the sheet would have to be cut into 6ft x 1ft strips to allow the staggering. This is a lot of cutting considering the length of my roof void. Or perhaps I'm being stupid, I just cut the ply into 2ft wide strips and secure down with 4 or 6 screws on each join?
Also, which is the lighter (in terms of weight) of the two materials and is the ply sufficiently rigid once cut into 6ft x 1ft or 6ft x 2ft strips?

A second hatch is unfortunately not an option. Current access is via a stairway to a larger squarer purpose made storage loft with standing room and from here you climb up into the 50ft triangular tunnel.
Creating additional access from the other end would require cutting a hatch 15ft up in the air (the height of the ceiling) which apart from being impractical would be aesthetically damaging to the room

Do like the idea about the great escape trolley. I would seriously consider that but how were the rails built?

 

[Flyfisher]

To start with we pulled the sand back from the face with a basin and rope but as the tunnel lengthened the engineers constructed railway lines made from beading strips taken off the walls of the rooms and a trolley with two wooden box's on it. The wheels of the trolley were made of wood, flanged and fitted with tin hoops, the axles were rods taken from some of the cooking stoves. A rope was fastened to either end and it worked like a charm

From: http://www.ateal.co.uk/greatescape/

Isn't the web fantastic?!

 

[Matt Green]

Whilst you can probably survive a 15' drop, and the boarding you are going to put down with distribute your weight, if I were asked to survey such a space I would go in with a harness and fall arrest system.

http://www.brandontoolhire.co.uk/directory/prodList.asp?idCategory=116

 

[Schoolmarm]

It is life or death important that when wearing a fall arrest system, SOMEONE SHOULD BE PRESENT AT ALL TIMES.

Cannot stress this enough. You can die if rescued wrongly after hanging in a harness and you ideally need to be got out of the harness as soon as you have fallen.
Plus if the harness or arrest components get caught on anything as you fall you will be in deep sh#t.

 

[MdB]

and having taken multiple falls onto rope systems, make sure there is give in the arrest system somewhere.