Opening Up Attic

[DirtSmuggler]

I'm looking to open up the attic in my personal home. I attached a rough sloppy sketch. The top is how the frame is currently in the attic. The bottom is how I would like to frame it to open it up. The dash lines are where the perpendicular part of the attic. Is this set up fine for the structural stability of the attic. And if so, why wasn't this done when built to give owners better attic space? If not, then what do i need to do to open up the space but still make it structurally stable?

It's a triangle prism roof with another triangle prism perpendicular to it. It's one unit in a building of 5 townhome with neighbors on both sides. [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1713902793/tips/DOC018_grbnuj.bmp[/url]

If i need to hire a structural engineer for this, what should I expect the cost to be? It's a 600 square space area.

 

[jayrod12]

You cannot do this easily. The original ones are trusses, the second sketch is not.

Yes you'd need a structural engineer. We cannot comment on costs as they are very locale dependent. Call around and ask for some quotes for the engineers around you.

 

[SWComposites]

Not only are you going from a truss to something that is not, you are adding significant load to the ceiling joists. Likely will need to reinforce both the roof rafters and the ceiling joists.

 

[JoshPlumSE]

I'll re-iterate what the other guys have said. You'll probably have to replace / reinforce just about all the framing in the exterior roof and the floor rafters. It can be done, but it could get pretty expensive.

Now, there are ways this could be less extensive. If it's easy to drop a column on one each side of the open space (perpendicular to your sketches), then you can move from a "truss roof" type of framing to a "Ridge Beam" system. You'd still probably have to reinforce the floor joists though.

 

[phamENG]

You need a new ceiling and a new roof if you want to open that up. Tear it down to the top plates and start over from there up. It'll be a lot easier and faster to do it that way than to try to do it from inside. You likely have 2x4 top and bottom chords with splices, so even going to a ridge beam won't work. The 'rafters' you'll be left with will be undersized AND have a pin in the middle, creating a collapse mechanism from the start.

 

[ChorasDen]

As stated, you've a tough situation. You've indicated this is a townhome type of construction, and I think you're in NJ? As such, what are the dimensions you are dealing with, i.e. what's the building width? What's the design snow load at your location? In my (limited) experience with NJ, the jurisdictions can be quite difficult to work worth, so you may want to talk with someone local just to get a feel for what you're up against before you try and move forward with any plans.

Additionally, in a townhome setup, you likely have architectural details that you need to be aware of, including rated firewall assemblies. If your ceiling is part of that rated assembly, you'll need to ensure a new system that gets installed is compliant with the requirements of the building type.

 

[JoshPlumSE]

The 'rafters' you'll be left with will be undersized AND have a pin in the middle, creating a collapse mechanism from the start.

Not sure what you mean by this. Top chords are usually framed as one continuous piece. Right?

 

[phamENG]

Not in most trusses. Shorter pieces of lumber are cheaper, so they'll run the a segment continuous over a panel point or two, then splice it with a butt splice and truss plate and run it up either over another panel point if the roof is large enough or up to the peak of the roof.

 

[jerseyshore]

Like you, I'm in the Garden State and I went to an attic in a Toms River community recently that looked very similar to your second picture even though it started out closer to your first one.

Needless to say, removing the middle webs of 40+/- trusses to get attic storage space was not a good idea. Felt like I had to duck when walking under that ceiling it deflected so much.

 

[RontheRedneck]

To address what PhamENG said about top chords of trusses -

Every plant I have worked at stocks lumber up to 20' long. It's almost always cheaper to use one longer board than to splice them. Adding splices means more plates and more labor.

 

[phamENG]

Ron - regional thing? Most residential trusses here that I've looked at have at least one splice in the top chord.

 

[RontheRedneck]

phamENG - It could be regional. Or maybe some truss plants only carry lumber up to 16' long.

 

[Althalus]

it is possible to do what you're intending. But you need to reinforce all the connection points.

Some questions:
1. Is the connection at the top a true truss connection? i.e. are all the pieces of wood sandwiched by some steel plates that have been factory pressed? If so, you'll need an engineer to figure out how to replace those plates when you remove the center struts.
2. Are the two top cords and the bottom chord a single piece each? Or are they cut at the plate locations? If they are cut, you simply cannot do what you are proposing. You may as well get an entire new roof.

 

[jerseyshore]

In older-ish homes or buildings, I always see single top chords around NJ, including the house I went to today. Not sure about new gable type trusses, haven't seen one in person in a while, but will have to check that out.

 

[XR250]

I have done these in-situ before but usually requires an interior wall that can be made bearing to cut the span of the floor system. Then is it just a matter of sistering the top and bottom chords - easy peasy (NOT)