jeff oakley Posted March 13, 2016 Share Posted March 13, 2016 Hi All, I know we have some bright people on here who work in the building trade. I have a small 60cm square loft hatch, which I would like to enlarge. This currently sits between two roof trusses that are preformed. To get the size I want it would mean cutting one truss to make a length of 120cm. Now obviously I don't want a sagging roof afterwards and it looks like an easy enough job to brace the cut joist to the two outer ones and to a new ceiling joist running the full length of the new opening. At present it is fully boarded and has stand up height in the centre, but you are restricted to what can be got through the hole. Not to store heavy things. Any obvious flaws, regulation wise or structurally or suggestions as to a better way to access the loft. Quote Link to comment Share on other sites More sharing options...
Mark (smokey mow) Posted March 13, 2016 Share Posted March 13, 2016 For a trussed roof the common method is to have doubled trusses either side of the structural opening and doubled trimmers to support the chord of the cut truss. However, trusses are not designed to be cut or modified in any way and the above would always be backed up by calculations either from the truss supplier or a stuctural engineer. If you do modify the truss make sure you are clear in how the truss is working as a whole and how the loads are being transferred and shared through all the structural elements, as its not as simple as just cutting or doubling the ceiling chord. As the works are a structural alteration you would also need Building Regulations consent. 1 Quote Link to comment Share on other sites More sharing options...
litcoat Posted March 13, 2016 Share Posted March 13, 2016 Are you making the hole 1200x600 or are you after 1200x1200? You can get pre made loft hatches with a ladder already attached that fits into the 600 width. I think you need to compromise, cutting roof trusses is definitely not recommended. Quote Link to comment Share on other sites More sharing options...
jeff oakley Posted March 13, 2016 Author Share Posted March 13, 2016 Hi it would be 600 X 1200 but after what Mark said it is probably more trouble than it is worth. Quote Link to comment Share on other sites More sharing options...
Terry Everall Posted March 13, 2016 Share Posted March 13, 2016 So long as you do not cut through the trusses and keep the width to the 600mm between them ( although some trusses are at 450 crs) then its easy as you just put transoms ( cross members joint adjacent trusses ) to suit the length you want Quote Link to comment Share on other sites More sharing options...
Mark (smokey mow) Posted March 13, 2016 Share Posted March 13, 2016 So long as you do not cut through the trusses and keep the width to the 600mm between them ( although some trusses are at 450 crs) then its easy as you just put transoms ( cross members joint adjacent trusses ) to suit the length you want that would be the better way to do it as it avoids cutting the truss and only the noggins need to be moved. Quote Link to comment Share on other sites More sharing options...
jeff oakley Posted March 13, 2016 Author Share Posted March 13, 2016 That would be okay unfortunately the hall landing runs across the truss not between. There is nowhere else it can go due to the layout of the house. Quote Link to comment Share on other sites More sharing options...
iain m Posted March 14, 2016 Share Posted March 14, 2016 If you need a bigger loft access you are obviously going to store some big items up there, beware the timber up there is to fix the ceiling to and your ceiling could will bow and crack. Also if insulated properly the space can reach some very high and low temperatures. I viewed a house with my eldest recently and all the upstairs ceilings were horribly cracked and bowed, I pointed this out to the agent, oh we know, the owner is working overseas and has been renting the house, his complete contents are up in the loft hence the 4 foot square trap!! Quote Link to comment Share on other sites More sharing options...
SootySport Posted March 15, 2016 Share Posted March 15, 2016 If you need a bigger loft access you are obviously going to store some big items up there, beware the timber up there is to fix the ceiling to and your ceiling could will bow and crack. Also if insulated properly the space can reach some very high and low temperatures. I viewed a house with my eldest recently and all the upstairs ceilings were horribly cracked and bowed, I pointed this out to the agent, oh we know, the owner is working overseas and has been renting the house, his complete contents are up in the loft hence the 4 foot square trap!! Oops! Quote Link to comment Share on other sites More sharing options...
Richard sheppard Posted June 9, 2021 Share Posted June 9, 2021 I have a loft hatch I nerd to put in in my hallway And the trusses do not work to the landing I only need to cut 1 bottom cord and then trim it up with x2 binders each side which will be 4 in total spaning over 3 trusses many thanks have you got any ideas I no you shouldent cut them but it just won't work what I have thanks Quote Link to comment Share on other sites More sharing options...
dombanks Posted June 10, 2021 Share Posted June 10, 2021 i recently fitted one of these into the loft space above the garage. they are designed to fit in between 600 centres. the length makes it great and all sorts of junk has gone up there. https://www.wickes.co.uk/Youngman-Timberline-Loft-Ladder-Access-Kit/p/183453?_br_psugg_q=loft+hatch i had to cut one section of the roof beam out to fit it as where i wanted it would have had one of the beams right down the centre of the hatch. i did a lot of reading around about it and (rightly or wrongly) i ended up making a rectangular box out of 2x4 that was just a bit bigger than the hatch. it was double thickness at the top and bottom so these were perpendicular to the truss direction and single along the sides of the box (running parallel). Just then cut the truss out, slotted this box in and then cut the plaster to suit. Quote Link to comment Share on other sites More sharing options...
Mark (smokey mow) Posted June 10, 2021 Share Posted June 10, 2021 14 hours ago, Richard sheppard said: I have a loft hatch I nerd to put in in my hallway And the trusses do not work to the landing I only need to cut 1 bottom cord and then trim it up with x2 binders each side which will be 4 in total spaning over 3 trusses many thanks have you got any ideas I no you shouldent cut them but it just won't work what I have thanks Please see my reply above in post 2. a trussed roof works differently structurally to a cut roof as all the components of the truss are interdependent, altering only the bottom chord will have a significant detrimental affect on the rest of the truss and rafter unless you understand the load transfer. you need to speak to a structural engineer and building control will need to see their calculations. 1 Quote Link to comment Share on other sites More sharing options...
Jim RS Posted June 10, 2021 Share Posted June 10, 2021 As others have said altering a trussed roof is extremely difficult and requires building reg approval. Modern roof trusses are designed to a very tight tolerance to minimise the amount of weight on the supporting walls and as such every member has an input to the overall strength, removing parts of these will require substantial strengthening and calculations to support the application. 1 Quote Link to comment Share on other sites More sharing options...
Dan_G Posted June 18, 2021 Share Posted June 18, 2021 https://www.diydoctor.org.uk/projects/enlarging_loft_hatch.htm I installed a big loft hatch from scratch in a previous 1930's granite house that required cutting of a joist. Pretty much did everything described in the link. Edit: this house had a rafter type roof not trussed. Quote Link to comment Share on other sites More sharing options...
Mark (smokey mow) Posted June 18, 2021 Share Posted June 18, 2021 1 hour ago, Dan_G said: https://www.diydoctor.org.uk/projects/enlarging_loft_hatch.htm I installed a big loft hatch from scratch in a previous 1930's granite house that required cutting of a truss. Pretty much did everything described in the link. That guide is fine for a traditional hand cut roof but not for a trussed roof. 1 Quote Link to comment Share on other sites More sharing options...
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