Existing hatch to access loft is approx 40x70cm running between 2 Fink trusses (W design?) at 43cm centres in a 70's bungalow. The truss bottom chord doesn't actually span that far from the proposed cut as there is a support wall approx 50cm from it (though bottom chord total length from bungalow outer wall plates is approx 11m).
I would like to cut a truss to make an opening of 80x70 so the loft space can be better accessed for storage and I can get bulky (but light) items like suitcases up in there. The cut would remove approx 70cm from the centre of the bottom chord of one truss and this would include the metal join plate.
I understand that there are risks etc associated with cutting a truss but there must be a way that loft hatch installers etc do it. The common practice seems to be to temporarily brace between 4 noggins (2 either side) of the truss to be cut front & back, then cut out the truss, and double up on noggins joining the cut truss bottom chord to the truss bottom chords either side. The "temp" brace can then be removed.
I'm not confident about this structurally. Am I right in thinking that any load movements in the cut truss will be outwards towards the ends of the span? If this is the case, is it not best to double up the bottom chord inner sides of the trusses either side so forces on the doubled up noggins abutt these added timbers to help distribute any forces along the neighbouring joist bottom chords? I will also be leaving the "temp" braces as they will become joists for floor boarding which screwed to these joists should also help distribute forces from the cut chord to the neighbouring trusses and those beyond.
What is the "normal" practice for cutting in such a scenario? I can't think of a better structural way of doing it but am open to ideas / experience.
I would like to cut a truss to make an opening of 80x70 so the loft space can be better accessed for storage and I can get bulky (but light) items like suitcases up in there. The cut would remove approx 70cm from the centre of the bottom chord of one truss and this would include the metal join plate.
I understand that there are risks etc associated with cutting a truss but there must be a way that loft hatch installers etc do it. The common practice seems to be to temporarily brace between 4 noggins (2 either side) of the truss to be cut front & back, then cut out the truss, and double up on noggins joining the cut truss bottom chord to the truss bottom chords either side. The "temp" brace can then be removed.
I'm not confident about this structurally. Am I right in thinking that any load movements in the cut truss will be outwards towards the ends of the span? If this is the case, is it not best to double up the bottom chord inner sides of the trusses either side so forces on the doubled up noggins abutt these added timbers to help distribute any forces along the neighbouring joist bottom chords? I will also be leaving the "temp" braces as they will become joists for floor boarding which screwed to these joists should also help distribute forces from the cut chord to the neighbouring trusses and those beyond.
What is the "normal" practice for cutting in such a scenario? I can't think of a better structural way of doing it but am open to ideas / experience.