Hello all,

So we have a cottage that is essentially 24 feet x 30 feet.  It's an old rafter roof system(not trusses) with 2 gable ends. 

We originally had 2 main walls spreading across the 30 foot span with separation for halls/entrances.  At one point we had  torn down one of the walls and the general contractor had put in 3 2x6 over a 16 foot span.  At first this wasn't that bad - but the ceiling originally had fiberboard(stuff used back in the 50s or so).  Later on, drywall was put on - overtop of the fiberboard.  So obviously some additional weight that wasn't necessary.

This eventually led to that 3 2x6 beam over that 16 foot span to sag(clearly wasn't a large enough beam should've been at least 3 2x8).  There was another beam added which was perhaps a 10 foot span again used 3 2x6, but this beam never did sag.

What we're looking to do is have an LVL beam installed to span the 30 feet.  Ideally we don't want any jack posts.  Does anyone have an idea if this is a possibility?  And/or what size of LVL Beam would be required for this?  The purpose of the beam would essentially be to hold up the ceiling across the cottage.

We've obviously torn down the drywall and fiberboard - but will only install drywall afterwards.

Any advice on specs, etc. would be much appreciated.

First, to the FOG!

There are a multitude of resources for LVL applications, but any lumber yard or home center should be able to help you size it appropriately. Your local building codes may actually specify the product you will need to install.

How about in pounds per square foot. I'm metric challenged. When I do a conversion I get 0.42 pounds per square foot.

Tom

You can do 30' with an LVL but its going to be big. A few thoughts...
- LVL manufacturers have span table PDF's for their different styles and sizes; go on their website, look up the table PDF, run through the combinations to find which one works for you; there are usually different options for height, thickness and type for a particular span
- that long of a beam is going to be pretty tall, make sure you pick a beam that still provides sufficient ceiling / walk through height
- it'll be heavy, you'll need mechanical help getting it into place; i.e. a crane, hydraulic hoists, jacks, etc
- you'll need to verify that your current end posts and footings can handle the load; putting that much load on 100 year old footings or 3" crap metal posts isn't going to cut it

You have 390 square feet of tributary load.

390x53=20,670 pounds
390x2.3=    897 pounds
Load        21567 pounds

21567/30=718.9 pounds per lineal foot the ridge has to support.

Looks like a 6-3/4"x19-1/2" Glulam.

You must be certain the ridge load is carried to bearing.

A local supplier should be able to verify what you need. They have software from the manufacture to check this.

The job will be very high on the difficulty scale. A crane is a must.

Tom

sorry.  picture didn't attach properly.

If the rafters are designed and built correctly that orange beam is totally unnecessary.

All of the roof weight transfers down the side walls, while the base of the rafters prevents the walls from spreading. You only need to certify the design of the rafters for proper load rating, fastening, etc. With the right materials you should be good with that design, WITHOUT any beam.

But, as suggested before,  get a lumber yard or truss company to run the their program on it for you. They'll do it for free. If you can't find someone to do it for you you might need to hire a structural engineer, but that's a lot of $$$ an I doubt you'd need to resort to that.

Unless there will be heavy load on the attic floor, for this application beam is not necessary. Just sistering floor joists with 2x12 or 2x14 should be enough.

Definitely call an engineer!   

Quote from: AzjaST on February 04, 2015, 06:42 PM

Unless there will be heavy load on the attic floor, for this application beam is not necessary. Just sistering floor joists with 2x12 or 2x14 should be enough.

Where do you get 2x14s?

Ask for Microlams (brand name, but kind of like 'Klenex') or LVL's - Laminated Veneered Lumber. They are available in sizes up to 5" x 26" or larger and lengths up to 52 feet.

Quote from: AzjaST on February 04, 2015, 06:42 PM

Unless there will be heavy load on the attic floor, for this application beam is not necessary. Just sistering floor joists with 2x12 or 2x14 should be enough.

Where do you get 2x14s?

Span tables 
But, seriously,  you can sister existing 2x6 or 2x8 with 2x10 or 12 with partial overlap to get 2x14. Or even better, convert each existing set of rafters and joist to truss just by adding king post and two struts. Anything spanning 30' will be monstrous; if 2 posts every 10' are possible than single 9 1/4 LVL will do but make sure these posts have way to transfer loads to the foundation.