Removing purlins

12938 Views 17 Replies 4 Participants Last post by Gary in WA, Jun 3, 2011

GottaDIY

Discussion Starter · Jun 3, 2011

Hi there. I'm in the process of remodeling a section of my attic into a bedroom. Or rather I'm in the final stages of the planning. Everything should be all set, however the purlins (I believe that's what they're called; the horizontal members going from one rafter to another on the opposite side of a gable roof) are in the way. They are 6 ft up from the joists. I'd like to relocate them about another foot up for headroom, for a total of 7 ft (I'd also be replacing them with 2 x 6s, because currently they are 2 x 4s). I am aware that this may be a problem (roof sagging). However I am also placing knee walls (should be about 4 ft high) at 5 ft from the eave on both sides. Would this be enough to provide sufficient support for the roof, altogether? The span across is 25 ft. Also, I plan to sheetrock the entire area (knee wall to rafter to purlin, across the purlin, down the rafter to the knee wall). Would hanging the sheetrock from the purlins cause any issues? I'm aware of how what needs to be done (insulation-wise and whatnot) otherwise. Attached is a picture. Thanks.

See less See more

1 - 18 of 18 Posts

sixeightten

· #2 · Jun 3, 2011

My gosh, those rafters are only 2x4??

Those things you refer to are called collar ties. Yes they do help the roof. Putting them up too high reduces their effectiveness.

GottaDIY

Discussion Starter · #3 · Jun 3, 2011

Ah, okay thanks. The collar ties are 2 x 4 (1-1/2" x 3-1/2") however the rafters themselves are something else (1-1/2" x 4-1/2"), it's weird. Would the knee wall help support, though?

sixeightten

· #4 · Jun 3, 2011

Technically, the knee wall will not offer true support because they themselves are supported only by the joists below. You could probably check with a string to see how much droop the ridge currently has. If it is pretty straight, I wouldn't hesitate to move those up maybe 6 inches, and upgrade them to 2x6.

GottaDIY

Discussion Starter · #5 · Jun 3, 2011

Okay, thanks again. One more thing, though. Would hanging sheetrock from the collar ties be an issue?

sixeightten

· #6 · Jun 3, 2011

GottaDIY said:
Okay, thanks again. One more thing, though. Would hanging sheetrock from the collar ties be an issue?

Not as long as they are adequately sized. For a 2x6 16" on center, I think you can span at least 11' on a ceiling joist. Make sure everything is properly ventilated and insulated prior to the sheetrock. If you will be adding any electrical, obviously that needs to be in as well.

GottaDIY

Discussion Starter · #7 · Jun 3, 2011

Okay, good. The span would only be roughly 6 or 7 ft if I raised the collar ties up a few inches. The pitch is pretty steep, so down below at the eaves it's 25 ft. But up at 6 ft, it's only barely 10 ft. Thanks, again.

kwikfishron

· #8 · Jun 3, 2011

Hope you don’t break your ceiling you’re now turning into a floor. How much weight do you think it will hold?

GottaDIY

Discussion Starter · #9 · Jun 3, 2011

That I'm not too worried about... I spent a whole day clearing out all kinds of crap from that section of the attic. A lot of "dead" weight (I know it's not actually dead weight, but for the amount of time most of that stuff's been up there, it might as well be considered as such) was up there. I don't think I'll be adding much by placing an open room in all of the stuff's place. The only things up there will be a queen sized bed, a small desk and computer, a dresser (there were two heavy ones up there before cleaning), a person, and a small table maybe? Though it did cross my mind.

sixeightten

· #10 · Jun 3, 2011

I recently worked on a similar attic. Existing joists were 2x4 on 24 inch centers spanning over 11'. Shot a laser across and saw that from highest to lowest there was a 3" diff. We ended up building another floor above the existing using 2x6 on 12" centers. Ceiling height changed from 8' to 7'4, but all in all it was the best way to go.

kwikfishron

· #11 · Jun 3, 2011

GottaDIY said:
That I'm not too worried about... I spent a whole day clearing out all kinds of crap from that section of the attic. A lot of "dead" weight (I know it's not actually dead weight, but for the amount of time most of that stuff's been up there, it might as well be considered as such) was up there. I don't think I'll be adding much by placing an open room in all of the stuff's place. The only things up there will be a queen sized bed, a small desk and computer, a dresser (there were two heavy ones up there before cleaning), a person, and a small table maybe? Though it did cross my mind.

How about the sheetrock? Where’s all the weight of that load going to transfer to?

GottaDIY

Discussion Starter · #12 · Jun 3, 2011

kwikfishron said:
How about the sheetrock? Where’s all the weight of that load going to transfer to?

True story... Actually, thinking about it, some of the sheetrock will be supported by the existing, load-bearing, exterior walls; some by the rafters (which would be transferred to the exterior walls below); and the rest by, of course, the floor (being attached to the 4 ft high knee walls on the perimeter). It would only be the approximately 32 lineal feet in all, and only half a sheet high.

sixeightten

· #13 · Jun 3, 2011

The floor loading is a valid point. If the floor sags, so does the rest of your work, and the ceiling below. Do some checking, and see what can be done to improve the performance of the floor. I agree that the loading of the drywall is minimal. The loading of furniture and people, a bigger concern.

GottaDIY

Discussion Starter · #14 · Jun 3, 2011

The existing joists are 2" x 6" and 16" OC with cross-bridging. I'm not sure of what else I could do... any suggestions?

sixeightten

· #15 · Jun 3, 2011

GottaDIY said:
The existing joists are 2" x 6" and 16" OC with cross-bridging. I'm not sure of what else I could do... any suggestions?

The span of the joists is what is important. You may be able to double up every third joist, but sometimes electric, plumbing, hvac makes this tough.
You should also check the existing floor with a string and see how much deflection is there already. This will probably be a real eye opener for you.

GottaDIY

Discussion Starter · #16 · Jun 3, 2011

sixeightten said:
The span of the joists is what is important. You may be able to double up every third joist, but sometimes electric, plumbing, hvac makes this tough.
You should also check the existing floor with a string and see how much deflection is there already. This will probably be a real eye opener for you.

I definitely hear you on that. The house was built in the 40's I believe, if not earlier than that. There are many places where things aren't square, plumb, or level. Now to find some string...

kwikfishron

· #17 · Jun 3, 2011

GottaDIY said:
I'm not sure of what else I could do... any suggestions?

You should call in a professional to develop a plan that you can submit for a permit, keeping your family and any subsequent owners safe and protecting yourself from future liability.:thumbsup:

Gary in WA

· #18 · Jun 3, 2011

I’m not an Engineer. I believe most of the roof load between knee walls will be transferred to the floor joists below. These should be sized for that load plus any floor load.

The floor is under-sized requiring doubling joists or larger ones. The rafters are under-sized for insulating value if not span. The collar ties should be in the top 1/3 of the roofs total height. You also need egress windows in any bedroom/or room up there. Egress stairs are also required. A permit is required as mentioned. Here is more info for your planning for the permitting; http://docs.google.com/viewer?a=v&q=cache:EJENK_uA9RQJ:www.cr-ar.com/pdfs/Building%2520Code%2520Changes.pdf+R602.3(1)+2006&hl=en&gl=us&pid=bl&srcid=ADGEESh311Kosslp7jsjp9WhUXxZsgSiyNaWb-eW0YminVwmPUavLlW75BKLoV9em4LFCAydmTGQlkUFOPm8AqHkRP5wLQGQQGkwyzAGtlN4D2DqCiCLwprOpEbvvjeGk6CEhyHiVdtK&sig=AHIEtbRa4Ah_IICPQ3BR1txlzU01V4JQIg

Joists in attic; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_5_sec002_par017.htm

Rafters/c.j.,/collar ties: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_8_sec002_par023.htm

http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_8_sec002_par018.htm

Egress; http://illowaicc.org/uploadedFiles/Illowa/Codes/Emergency Escape Rescue Openings.pdf

Gary

1 - 18 of 18 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.