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Oak Truss Size Detail?


ashthekid

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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?

779316E7-BBC5-4820-B8E5-E57FC17C1B37.jpeg

7FC035FC-6F40-4868-BDBC-097787A0CAE8.jpeg

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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.

 

 

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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?

779316E7-BBC5-4820-B8E5-E57FC17C1B37.jpeg

7FC035FC-6F40-4868-BDBC-097787A0CAE8.jpeg

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.

 

 

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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. 

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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. 

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@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.

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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

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