Loft storage project question

[Chri5]

Hi Guys, about 8 years ago we had a loft conversion.

We always planned for storage but I nver got round to doing it, and since SHMBO wants the loft decorated the time is ripe so to speak.

Here's the external view, the area of interest is the inside of the front gable.

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• Chri5
• 13 Oct 2012
• 1

Here's a very rough line drawing from a side view, lhs is the gable which is lower than the roof ridge line. The red boxes donate some of the main steel support

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• Chri5
• 13 Oct 2012
• 1

When they converted the loft we made hatch provision to access the dead gable space and today I took half of the hatch size out to get in a measure up.

The store room area will always be a simple store nothing more and the plan is to lay celotex on the existing structure, then tg 22mm chipboard, lag all areas and plaster board over to make the area sort of dust proof.

Now I can work round the existing structure, but I have been wondering if I could encourage some more space by removing what looks like unnecessary diagonal rafters that would have supported the gable prior to the loft conversion.

Here's half the intended access point

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• Chri5
• 13 Oct 2012
• 1

Now with your head looking in to the gable, you see the picture below. In the far ground is the internal brick face of the gable and between the camera and the brick face are the rafters in question.

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• Chri5
• 13 Oct 2012
• 1

Looking from the gable brick face back towards the access hatch you see the rafters better

Rafters at the top towards the ridge of the roof and the sub roof steel. Its the 3 central ones that Id like to cut out.

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• Chri5
• 13 Oct 2012
• 1

Lower down

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• Chri5
• 13 Oct 2012
• 1

and finally where the rafters join to the old joists between 1sr floor ceiling / old loft floor level.

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• Chri5
• 13 Oct 2012
• 1

So any ideas, am I playing with fire even thinking that the three rafters I'd like to take out can be removed?

My (uneducated) logic is the prior to the loft conversion and the 'new' structural integrity created by the steels the rafters would have been essential on a full wood roof structure.

But now since the steels take the loads, and since there is load support between the front floor steel and the roof line they are simply redundant.

Thanks for reading,

 

[chickenlips]

Those rafters you want to remove look like they are supporting the layboard which the gable rafters are fixed onto. My gut feeling is no they cannot be removed without finding sufficeint support for the valley board. .

 

[tony1851]

Chicken lips is right in that builders would often use the rafters of the main roof to support thin layboards, which in turn support the rafters of the bay roof.
The middle 3 rafters going down below the level of the steel may appear to be redundant but you need to be careful.

I did exactly the same thing several years ago (cutting out 3 rafters below a purlin to get into the roof void of a later extension). When cutting out the last 2 rafters, the saw kept jamming. I was forgetting that the the whole assembly of ceiling joists and rafters forms a rigid triangle, and once I'd removed the connections between the rafters and old ceiling joists, the opposite roof slope was tending to pull away (the rafters were obviously in compression). To reduce any further tendency to spread, I glued and screwed large sheets of plywood across most of the ceiling joists to make the ceiling a rigid horizontal diaphragm, continuous with the part where I'd not cut the rafters away.

Sorry I've gone on a bit but the pronlem is not easy to describe. I should think carefully about this. Could you just take out 1 rafter? That would at least give some additional space.

 

[Chri5]

Thanks guys fo the replies.

I could get away with removing one rafter to give some head room in the store. Quite a few of the other loft converted terraces on the street have got the gable area as part of the conversion living space.

As I mentioned that is not my intention and I had hoped that supporting the three cut back rafters above the studs that get support from the steel at floor level would be enough.

I weary of being a silly billy and doing something that appears fine and then in week, month or years time turns out to be a disaster.

I had thought that cutting back the three rafters above the entry area and then fitting heavy duty angle brackets or a lump of 4 x 4 as a stop buffer would have done the job. I could also tie the remains of the rafters together with a fabricated plywood plate.

Something like

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• Chri5
• 14 Oct 2012
• 1

If none on that is feasible who is the most sensible source for pro knowledge, a good roofer or a structural engineer?

 

[tony1851]

Chris.

Putting plywood where you suggested would not solve the potential problem I outlined. This is my fault for not explaining it clearly, so I've attached a couple of sketches to hopefully explain the issue

The top sketch shows the normal situation, where the compression in the rafters is balanced by the tension in the ceiling joists, and the whole thing remains stable.

The bottom sketch shows the situation when part of the rafters are cut away; the tension goes out of the ceiling joists and, in theory, there is nothing to stop the opposite slope from pushing outwards. In my case, with 3 lower rafters removed, I glued and screwed ply sheets -shown red - connecing the freed ceiling joists to those on either side, so making (hopefully) a rigid horizontal diaphragm.

In your case, you have additional joists and boarding for the loft floor, plus a flat roof, both of which will act as horizontal plates and considerably enhance rigidity. In these circumstances you might, on reflection, be OK.

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• tony1851
• 14 Oct 2012
• 1

 

[chickenlips]

Just looked at your diagram again in your 1st post and there is a way to do it.
Your Layboard, which is supporting your rafters in your gable, will have to be turned into a hip layboard.

Basically rather than sat flat, the layboard needs to be turned and sat on edge to give better support to the rafters in your gable. This would happed over where your existing steel is down to the ceiling.

 

[HERTS P&D]

Easy, tell the wife that it can't be done without weakening the whole roof. She has the loft conversion as she wanted more room.

Andy

 

[Chri5]

Hearts drainage is that a professional opinion or just a guess that it can't be done

See I take the view that can't isn't a word and although she wants it done, so do I. The main failing of loft conversions is loss of space. We have elder kids that want to hag on to 18 years of stuffed toys. I have a wife that doesnt have room for all her clothes in one location, so she brings stuff out for the season required.

There's 15m sq of storage for stuff that's under beds, stuffed in airing cupboards and what has already been mentioned, so no matter what it will be used, it's all about how much access there is going to be.

 

[HERTS P&D]

The question I would ask is why didn't the builders add the extra space when doing the loft conversion.

I have worked on many loft conversions and have seen when things went, the cost of repair went through the roof.

The best thing to do is get a structural engineer to have a look at it and take it from there.

Andy

 

[Chri5]

Thank you Tony and Chicken lips for your time and helpful remarks.

Your Layboard, which is supporting your rafters in your gable, will have to be turned into a hip layboard.

Basically rather than sat flat, the layboard needs to be turned and sat on edge to give better support to the rafters in your gable. This would happed over where your existing steel is down to the ceiling.

I'm sorry and I have spent an hour trying to find some google reference to hip lay board and I can't. I understand the lay boards x 2 run from the centre ridge down, and these flat plates support the rafters in the gable.

Could you try and explain?

Chris.

Putting plywood where you suggested would not solve the potential problem I outlined. This is my fault for not explaining it clearly, so I've attached a couple of sketches to hopefully explain the issue

The top sketch shows the normal situation, where the compression in the rafters is balanced by the tension in the ceiling joists, and the whole thing remains stable.

In your case, you have additional joists and boarding for the loft floor, plus a flat roof, both of which will act as horizontal plates and considerably enhance rigidity. In these circumstances you might, on reflection, be OK.

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• tony1851
• 14 Oct 2012
• 1

That was very kind of you to put the effort it.

I understand that the roof triangle was broken, that the dormer back square is supported as a rigid box. The front house lower steel as seen in white fire proofing paint in the early pictures is there (I think) to support the new loft floor level AND support the front rafters since the triangle rule is broken by the dormer.

I also understand that the main rafters support the layboard for the gable rafters that make the valley zone.

The three rarfters I want to remove seem to have no great supporting role as far as the valley, or the layboards that support tha gable rafters. Are concerned.

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• Chri5
• 13 Oct 2012
• 1

The centre one appears to offer no support at all

The LHS and rhs of centre offer support at a point that could remain and that would be easy enough to fix some hd plates, brackets or whatever fixing is suggested.

So what do you say guys, yes or no, or yes with actions?

If all else fails I could work round, leave it in situ and ask a sons friend at Xmas who is studying structural engineering (although he might still be at the Lego stage of his knowledge base).

If the matter can't be resolved, who would you suggest I call it, a roofer, a builder or a structural engineer?

(again) Thanks for time.

 

[chickenlips]

A Hip Layboard is a term used more commonly in Trussed rafter roofs, more commonly when creating a walk through valley in an attic or raise tie roof construction. Which is in essence what you are trying to do here.

Basically a hipboard in a valley construction, where the valley is not supported underneath by rafters running perpindicular the valleyboard stops and is started again continuing on edge with the rafters fixed to the side of the hipboard.

That help lol ?

would be easier if I was at work and could easily post up some details.

 

[Chri5]

The question I would ask is why didn't the builders add the extra space when doing the loft conversion.

I have worked on many loft conversions and have seen when things went, the cost of repair went through the roof.

The best thing to do is get a structural engineer to have a look at it and take it from there.

Andy

Thanks for that. The builders stated that the works hadn't been included on the pp submission. That was one of a few issues that ended up with them finishing at 1st fix and me done the rest.

They did a good job, but they didn't like following the agreed spec and hated me being around to project manage. Silly things like trying to invoice £7k for steel materials when I ended up paying direct for £2.5k

 

[Chri5]

The question I would ask is why didn't the builders add the extra space when doing the loft conversion.

I have worked on many loft conversions and have seen when things went, the cost of repair went through the roof.

The best thing to do is get a structural engineer to have a look at it and take it from there.

Andy

Thanks for that. The builders stated that the works hadn't been included on the pp submission. That was one of a few issues that ended up with them finishing at 1st fix and me done the rest.

They did a good job, but they didn't like following the agreed spec and hated me being around to project manage. Silly things like trying to invoice £7k for steel materials when I ended up paying direct for £2.5k

 

[Chri5]

Basically a hipboard in a valley construction, where the valley is not supported underneath by rafters running perpindicular the valleyboard stops and is started again continuing on edge with the rafters fixed to the side of the hipboard.

That help lol ?

would be easier if I was at work and could easily post up some details.

Get back to work immediately

I think I'm with it, if you could support your knowledge with some link or a picture, it would help it all sink in.

I won't tell your boss, if you are the boss- don't tell yourself.

 

[chickenlips]

This is what I was refering to. The layboard is turned on its edge to support the rafters so that a clear 'walk thro' area is created.