ashthekid Posted May 7, 2021 Share Posted May 7, 2021 No sure if this is the correct group to be posting on but I’m changing a couple of softwood trusses to Oak hardwood. They are exposed trusses. Same dimensions for span(8073mm) and height(2352mm) etc but does the thickness of the oak wood itself have to change and if so by how much? Link to comment Share on other sites More sharing options...
Mr Punter Posted May 7, 2021 Share Posted May 7, 2021 Because it is structural you will need calcs for these. Best to contact a truss designer / manufacturer. 8m span is large. There are lots of online design / quote sites so you will get some idea of what you can do and what it might cost. Link to comment Share on other sites More sharing options...
Gus Potter Posted May 7, 2021 Share Posted May 7, 2021 3 hours ago, ashthekid said: No sure if this is the correct group to be posting on but I’m changing a couple of softwood trusses to Oak hardwood. They are exposed trusses. Same dimensions for span(8073mm) and height(2352mm) etc but does the thickness of the oak wood itself have to change and if so by how much? If you are keeping the same geometry then the oak will perform better than the soft wood. Roughly, if you think about a bit of soft wood it is made up of mainly cellulose with air gaps in the cells, it has a certain density. Oak is more dense than softer woods so you get more material and less air... thus it is "stronger". In principle the members should be fine. However, it is the connections between the timbers you need to have a look at just to make sure they are ok. If you are swapping a prefabricated softwood truss with nail plates say for an oak truss then it's worth a check on the connections. Alternatively it may be that you have a traditional cut timber roof, nailed, maybe a pole plate on the wall head. All this may need is a quantative check on the connections. In other words you can say.. the timber has a higher grade than the existing, calculate the capacity of the existing fixings and provide new fixings equal or better than the existing. Link to comment Share on other sites More sharing options...
ashthekid Posted May 8, 2021 Author Share Posted May 8, 2021 And an online oak trusses designer would be able to help with all of this or do aI need to go back to a structural engineer? I literally thought it was a case of changing the softwood to a stronger hardwood in oak and it be the exact same sizing/thickness etc because it’s a better material to support all the various loads and pressures. Link to comment Share on other sites More sharing options...
tonyshouse Posted May 8, 2021 Share Posted May 8, 2021 Oak is special, it is very strong in tension - the supplier should help with calcs Link to comment Share on other sites More sharing options...
Russell griffiths Posted May 8, 2021 Share Posted May 8, 2021 What about the load on the walls supporting theses trusses, I would expect the oak ones to weigh 3 times the weight of the softwood ones. Link to comment Share on other sites More sharing options...
ashthekid Posted May 8, 2021 Author Share Posted May 8, 2021 So far nobody online will provide the exact measurements for oak and are requesting fresh calcs from Structural Engineer. Little bit frustrating as my structural engineer is quite slow in coming back to me. Link to comment Share on other sites More sharing options...
ashthekid Posted May 8, 2021 Author Share Posted May 8, 2021 @Russell griffiths The walls are timber stud frame so can easily be reinforced or modified to take the extra weight. Link to comment Share on other sites More sharing options...
ashthekid Posted May 8, 2021 Author Share Posted May 8, 2021 @tonyshouse Supplier wise, who would you recommend to use to get a quote and calcs? Link to comment Share on other sites More sharing options...
tonyshouse Posted May 8, 2021 Share Posted May 8, 2021 Someone local, there are several oak framing companies near me, Link to comment Share on other sites More sharing options...
PeterW Posted May 8, 2021 Share Posted May 8, 2021 Are these structural or decorative ..? How can you only be replacing 2 to be visible ..?? Link to comment Share on other sites More sharing options...
ashthekid Posted May 8, 2021 Author Share Posted May 8, 2021 @PeterW Both structural and decorative. It's a conversion project that includes a whole new timber frame and roof section built within old walls with vaulted ceilings - there is nothing above it. The new inner skin is a timber frame with only two trusses required by structural engineering drawings but our original design has them in softwood. We now want to make them more of a feature and know how much better it will look in oak finish. I assumed with oak being stronger than the measurements and sizes of the trusses would remain the same but the people the contractor is using to create the trusses are requesting new calcs now from the SE. Link to comment Share on other sites More sharing options...
ashthekid Posted May 8, 2021 Author Share Posted May 8, 2021 Out of curiosity because of oak moving so much in my experience, is there a softwood that could very easily be disguised or treated to look similar to an oak finish? Link to comment Share on other sites More sharing options...
PeterW Posted May 8, 2021 Share Posted May 8, 2021 I prefer Douglas Fir for this sort of stuff and it doesn’t need stainless fixings. Also easier to get in long straight lengths. Will still set you back £2-2.5k each but slightly cheaper than oak. https://www.douglasfirtimber.com/queen-trusses/ Link to comment Share on other sites More sharing options...
PeterTweeter Posted May 15, 2021 Share Posted May 15, 2021 That's not a house truss - more like a bridge truss!! Seriously, the pitch is c30deg, quite shallow for a king post truss. Typically, I have built redwood trusses like these, but the pitch is 9/10, ie 42deg. Your SE is having a laugh, the deflection would be something else. I would go with PeterW's suggestion & go for douggie fir & something like a Howe truss - much more like a bridge truss, cos 8m is a stretch! The truss builders quoted will have a much better handle on the shape/material - trust them. Cheers Link to comment Share on other sites More sharing options...
PeterTweeter Posted May 15, 2021 Share Posted May 15, 2021 (edited) BTW - which forest is going to yield an 8m+ lump of straight oak? Unless, of course there is a join!! Even more of a deep intake of breath. Go for the DF - just saying. Edited May 15, 2021 by PeterTweeter Link to comment Share on other sites More sharing options...
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