I have a nearly 100 year old house that through time has been modified again and again. From what I can tell, around 1910-1920 a ~25x12 addition was put onto the back of the house to allow for the installation of plumbing. They only put on a first floor and made the roof into a deck. Then, sometime later (~1950) someone decided to turn the deck into a second floor addition. They never finished the job. What I have now is unfinished walls that have studs around 20" on center, lots of storm windows, and roof trusses that really aren't trusses. Basically the roof trusses are just really long 2x4 around 25' long and 20" on center. This is causing the roof to now sag and I am getting concerned that if I don't fix this soon a heavy winter snow can bring down the roof.
We have plans to complete this room and make it usable but I would like to get the trusses fixed first. Our hope is to one day have vaulted ceilings in the room so we would like to convert the 2x4s into a scissor truss of some kind.
Can I turn the existing 2x4 into scissor trusses? Does anyone know of a good book, calculator, website, etc. that will help design the new trusses? Or is this a really stupid idea?

 

No, it is not a stupid idea, it is done all the time, it is just that you are kind of off on the wrong track. The easiest thing to do is just take off your old roof, and install new cathedral trusses. No figuring, no calculations, no nothing. All you need is the distance between your sills, and what pitch you want on your roof. Taking off an old roof is easier then it looks. You have rafters in your house, and they cannot be converted. I am getting ready to do this exact thing on a house remodel. In fact they called today and said my trusses are in. Just my thoughts. Good Luck

 

Actually, there are no rafters in this part of the house. Just really long 2x4' that go from the wall to the peak of the roof. Can these be converted?

 

No, I am sorry but they cannot be converted.

 

ebne0018,

the easiest fix is to install a new ridge beam at the center under the existing. then run new rafters under the existing roof to the new beam. Over size these lower rafters and then you can kick braces from the lower rafters to the overspanned (e) rafters thus creating a scissor type truss under the existing roofline.

I hope this helps

Brian Garrison

 

ebne0018,

The suggestion by Brian is not recommended nor should it been suggested that you can do this. This is misleading information that has major consequences, both from a structural standpoint and from our Forum Policies standpoint. There are limits to what can be suggested to members and this crosses the line.

Lets start off with this,

1. Your home is old - this causes some concern altering existing structure where stability and structural integrity will be questioned.
2. The span is too large for existing lumber
3. The existing lumber is too small
4. Getting a beam in while supporting the existing rafters is virtually impossible.
5. Trying to manufacture a scissors application within the space is difficult yet can be done - Problem - EXPENSIVE and TIME CONSUMING
6. The amount of work required to do what was mentioned is labor intensive
7. You need an Engineer to approve any such alteration as per Brians method.
8. You need a Building Permit !

The suggestion is a major feat that requires deep pockets!! (Money) and if it could be done at all. I doubt it can.

If you want vaulted ceilings, purchase pre-man. scissor trusses and be done with it. You're going to have to replace the roof anyways if you try and make-do. These will go up fast and be shingled and done within 3 days MAX!!! This is providing you have a good crew out there. One doing demo and the other coming behind and installing new trusses! A crane works best, this decreases the time the roof is open. It is not the time to worry about how much a crane costs!!

I strongly go along with Jack on total roof removal, install pre-manufactured roof trusses that are designed for the span and roof load requirements. In addition these are approved, stamped by an Engineer to allow for a Building Permit.

You'll be saving money in materials, labor and most of all the time that this structure will be open to the weather.

Brian's intentions are good but we need to keep things in context.

Please do this the right way!

 

I'm with Doug and Jack -- go get trusses!!