Boading out a detached garage

24 Sep 2013
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United Kingdom
Hello all,

I have seen numerous posts on similar topics but I just wanted to double check a few things with pros before I proceed and have the roof off...

I am in the process of trying to board out my garage roof in order to have some additional storage space. I will say at this point that I am only looking to store some old boxes, christmas decorations, the odd suitcase with out of season clothes etc. It does not need to support a grand piano. Just the usual household clutter and my weight occasionally as I move stuff around.

The garage is a single car design, approximately 7m x 3.6m and is detached from the house. The house is a 2012 vintage newbuild so the garage has the usual truss frame design with 3x1.5 joists.

I want to board it out with the usual 18mm T&G chipboard panels but I realise the roof is designed to support itself and not any additional weight. As such I intend to add additional joists in between the roof ones so the boarding out is supported by these and not by the roof joists.

If I use the normal structural tables I am looking at 7x2 joists for a 3.6 span at 400mm centres. Bearing in mind I am just looking for some additional storage space and this will not be a habitable area or one that will support anything other than me occasionally and the odd box of bits is this overkill? Can I get away with anything smaller? Ideally I would like to use as small as possible to keep the cost down and also to maximise the height in the boarded out area.

For added info the garage is double skinned brick with a timber cap. I was just going to sit the joists on top of this and hold in place with right angle brackets. Or should I use joist hangers?

One final question. There is a couple of very thin planks running length ways down the building which look to tie the truss rafters together. This is a pretty shoddy piece of joinery and is not even fixed to all of the trusses. If I use bigger additional joists I am going to have to remove these pieces. I was planning on just using the chipboard to keep it all tied together or move these lengthways timbers up onto the apex part of the fame? Mistake or not?

Thanks in advance for any help!
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it sounds like your going really overkill just to store a few boxes?

just simply sit a big sheet of 18mm ply over the trusses?

it will take the weight of a person, and a few boxes i'm sure!

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