Roof Engineering Question

[Fotheringay-Phipps]

I have a question about the structure of my attic roof. As it stands now, the roof beams are given some additional support from beams (2x4) that are parallel to the floor and which are nailed into the roof beams on either side, about half-way between the attic floor and the peak of the roof. IOW the roof is structured like an A, although the crossbeams are about 1 every 4 linear feet (versus the roof beams themsevels, which are 16" apart).

The purpose of these cross-beams is presumably to stop the weight of the roof from pushing the roof down and the exterior walls of the house apart.

However, I would like to make some more use of the attic space, and these cross beams are in the way. So I'm casting about for another method of achieving the same support in a less obstrusive manner.

Most specifically, I'm wondering if I can remove these beams and instead nail vertical beams into the ceiling beams and into the floor joists of the attic. So that instead of supporting the roof by binding the two halfs of the roof to each other, I would be supporting it by propping up the roof against the 2x8s that form the attic floor.

Does this make sense? Does anyone know and/or is there some way for me to determine this without hiring a structural engineer?

[Sharp Dressed Man]

Yeah and after you get some expert advice on that one here, be sure to ask for some added suggestions on how to restructure your retirement portfolio, what you should do about your most serious medical problems, how to relate to your wife and how to raise your children.....and do whatever they tell you

[hallerb]

you have roof trusses, theres no way to change them without a structual engineer. soory

[BobK207]

Yes, if you have a simple roof structure (impossible to tell from your description) you MIGHT find a knowledgeable contractor who could do simple & safe modifications.

If you have modern trussed framed roof, cutting / removing / changing members could compromise the roof system.

cheers Bob

[nicksanspam]

There are many ways. Using an engineer is a personal choice.

Nick

[Paul Franklin]

Well, you can hire one, or you can become one, or you can take a chance. How lucky do you feel?

What you are describing sounds like collar ties. And you're right, they are there to help resist the outward force on the walls caused by the weight of the roof pressing outward on the top plate of the walls. The roof doesn't just press down, it also presses out because of the shape.

There are at least three common ways to resist the roof forces.

You can have a structural ridge beam. The ridge is the top peak of the roof. With a structural ridge beam, a heavy, strong beam runs down the ridge and is supported at the ends (and sometimes at one or more points along the length) with strong enough structure to carry the full load down to the foundation. With the ridge beam holding up the center of the roof, the rafters no longer push out on the walls.

You can have a stick framed roof, with a thin ridge board, and rafters running down to the top plate of the walls. With this, the attic floor joists (ceiling joists of the floor below) run all the way from the rafter ends on one side to the rafter end on the other side. These joists essentially form a triangle with the two rafters and the joist resists the outward force of the roof rafters. Sometimes it isn't possible for the joists to run all the way from one rafter end to the opposite rafter end. There may be an opening in the floor, or the framing pattern doesn't allow this to be done. Collar ties can help resist the outward load in this case. This is probably what you have, based on your description.

The third common roof framing method is to use trusses. Doesn't sound like you have them based on your description.

What you are proposing to do is to convert a stick framed roof to a sort of structural ridge. It can be done, but not the way you are proposing, and not without proper engineering. What you propose will transfer roof load to the center of the floor joists. If there isn't adequate supporting structure under the center of the joists, you will create a dangerous situation.

This isn't the kind of project to take a chance on. The last thing you want to hear is the sound of nails ripping out of lumber as your roof collapses the first time it snows or you get a big windstorm.

HTH,

Paul F.

[ransley]

Vertical onto a ceiling joist will push down on that ceiling, a load bearing wall might be better, do you get much snow.

[MLD]

And the load from the roof truss would be transferred to the ceiling beams instead, pushing down on them. Worst case scenario would be the collapse of the ceiling. Better just utilize what space you have and just duck your head as you move through the attic. MLD

[Ivan Vegvary]

Paul, while I have seen plenty of layouts and diagrams, I have never seen a better VERBAL description of roof framing than how you wrote it above. BTW I am a licensed engineer. Your description was concise, to the point and accurate.

Ivan Vegvary

[tbasc]

So, Ivan, do you think he should use an engineer? T

[tbasc]

I am just finishing a project that included work to repair a roof that had its collar ties removed. The fix included using chains and winches to pull the walls back to vertical and fabricated steel plate connectors at rafter ends. It took some time (weeks) to do this.

T

[EXT]

From your very brief description, it may be possible, however as in many things it is all in the details, which you do not give. Also since you do not know the names of the roof parts and their uses, it appears that you are not familiar with construction. This also can be a problem.

We cannot see these details from here along with the construction materials and sizes used. Many of us are not qualified to give their opinion either. You need a qualified person to examine your roof and provide plans on any modifications that are appropriate.

[Paul Franklin]

Thanks Ivan, appreciate the kind words.