Very Big Knot Holes in Roof Trusses

Hi knots can be treated with 'knotting' this is a brown thickish liquid Which you simply brush onto the knot. More likely to find it at the builders merchant than diy stores. If you have a particular resinous knot ( one that oozes) drill or rout out and fill with two part filler sanding down before painting in the usual way.

joybell knot holes are different to live knots knots are classified in many distinctions and if knots are evident and have fallen out of the timber these are called dead knots , these mean that the timber has become severely weakened and it also means that your timber hasnt been electronically or visually graded for sale or to purpose please understand that knots in trusses present major problems when used and technically can be unfit for use if the knot is so large , or there is a cluster of knots say over 150 mm or so on over a linear metre your problem stems back to the manufacturer and i suggest you request a visit for likely replacement if the size matchbox is the true size described remembetrusses can take good loads on their manufacturers edge and all are held in tension and compression when loaded with tiles or bitumen trust this helps you with your decision

Yes, I agree with LORDS CARPENTRY AND JOINERY. You can also strengthen beams in location of knot holes by suitable flat steel bracket as a faster solution.