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Old 08-23-2012, 09:07 AM   #16
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Attic catwalk design


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Originally Posted by tony.g View Post
............
That's an awesome drawing....thanks!

I am not a carpenter but I take it that you're suggesting the 2x2 strips on the inside is basically making a gusset design which is more secure than my idea of using some 1.5x1.5 metal framing brackets (L-bracket) at the topside of the original joist where the 2x4 post would sit. I can get metal L-brackets for 50 cents each and they accept 2 screws on each face. I thought that might be simpler and would sufficiently keep the 8" post from moving on top of the joist.
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Old 08-23-2012, 09:34 AM   #17
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Attic catwalk design


You can use 1.5" x 1.5" brackets to secure the 'posts' to the top of the existing ceiling joists, but presumably you would also need some to fix the top rails to the posts. You would be fixing these from underneath, which would be difficult to get to.
If I've read correctly and the brackets are 1 1/2", tbh that is not very big and the screw fixings will be small and close together - i'm not sure that would give you a good, firm fixing.
If the brackets are 50c each, and assuming you used 4 per 'post' (ie 2 at the top and 2 at the bottom), I wonder if a few 8ft lengths of 2x2 might work out cheaper, and they would probably give you a firmer fixing as well.
The main point to watch is lateral movement - you don't want the structure lozenging sideways - that's why i suggested a few plywood pieces going across the assembly, screwed to the posts and a tight fit between the ceiling joists.
(i'm not into HVAC so don't know about the other bits! good luck with it).
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Old 08-23-2012, 09:53 AM   #18
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Attic catwalk design


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I've built cat walks in attics and it is usually best and most simple to build a 2x10 cat walk 16 to 24" wide with a few 2x10 spacer blocks about every 4'. A cat walk I did recently had the same situation with insulation already in the attic and the insulators were on the way to do blow in for the entire attic. We built the catwalk and insulated inside of it with r 30 before putting the plywood on top, that way when the insulators came we did not have to go back into the attic space to put down the plywood afterwards.
So you're saying just 16 to 24" pieces of 2x10, laid perpendicular to the existing joists. Do you fasten the 2x10s with metal L-brackets to the top of the joist?

Reason I had devised this 2x4 "arches" design was because my gut was the extra weight of the 2x10 pieces might be a bad thing. So I should have taken pen to paper earlier......I just googled weights per foot and I basicaly calculate that a 18" section (I'd think that should be fine to sit perp to 16" OC joists) of 2x10 is approx 5 pounds while my "arch" made of 2x4s is 3.8 pounds. That doesn't count the various screws needed to fasten together the 3 piece arch vs a single solid piece of 2x10....probably nomimal but the deck screws aren't weightless either.

Ok so basically I over-thunk it! I can't imagine that an extra pound on each riser is going to kill my ceiling over time, given that this is a limited catwalk and not a full attic floor build.

Sorry to keep asking questions but I enjoy learning about this stuff too and want to do the right thing

1) did you use plywood deck on top of the rafters or can I just use 2 1x8s?

EDIT: I did the calc and I can get 24 linear feet of 5/8" plywood deck from one 4'x8' sheet and it would cost $15 if I get OSB Sturdifloor or $20 if I get CDX plywood. For 24 linear feet I'd need 6 1x8 boards which would cost $38. So the cost is almost 2X - there's my answer. 1x8 pine board is a tad thicker but I'd assume 5/8" plywood is sufficiently strong for my needs. Can I get by with 1/2" OSB or CDX or is that going to be too bendy? Or do I need to go 3/4" OSB or ply? I'm lost on what the various "span ratings" etc mean in practice for a 180 pound person walking on a catwalk.....

2) can I get by with 30" or even 36" spacing between the 2x10 risers? I have a single 1x8 board in my garage and I stood on it last night....I weigh 180 pounds and it felt very solid with 30" spacing between blocks underneath it. I don't want to over-spec this with 2x10 pieces every foot or whatever because while that would certainly be stable and I could drive a truck on it, I'm adding extra materials cost and dead weight with each 5 pound riser that is unnecessary....

Unfortunately I prob can't finish and insulate the catwalk before the guys come because they are doing air sealing and they'll need to get at some conduit protrusions as well as some can lights and I don't want to finalize something that is then somehow in their way. I'm thinking I'll just install the risers and then they can blow the stuff around, then I'll come back and add the top deck.

Last edited by Hogan773; 08-23-2012 at 10:40 AM.
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Old 08-23-2012, 11:45 AM   #19
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Attic catwalk design


If you are putting 2x10s across the ceiling joists, you would bigger/stiffer brackets than 1.5" to keep them vertical.
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Old 08-23-2012, 01:11 PM   #20
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Attic catwalk design


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Originally Posted by Hogan773 View Post
So you're saying just 16 to 24" pieces of 2x10, laid perpendicular to the existing joists. Do you fasten the 2x10s with metal L-brackets to the top of the joist?

Reason I had devised this 2x4 "arches" design was because my gut was the extra weight of the 2x10 pieces might be a bad thing. So I should have taken pen to paper earlier......I just googled weights per foot and I basicaly calculate that a 18" section (I'd think that should be fine to sit perp to 16" OC joists) of 2x10 is approx 5 pounds while my "arch" made of 2x4s is 3.8 pounds. That doesn't count the various screws needed to fasten together the 3 piece arch vs a single solid piece of 2x10....probably nomimal but the deck screws aren't weightless either.

Ok so basically I over-thunk it! I can't imagine that an extra pound on each riser is going to kill my ceiling over time, given that this is a limited catwalk and not a full attic floor build.

Sorry to keep asking questions but I enjoy learning about this stuff too and want to do the right thing

1) did you use plywood deck on top of the rafters or can I just use 2 1x8s?

EDIT: I did the calc and I can get 24 linear feet of 5/8" plywood deck from one 4'x8' sheet and it would cost $15 if I get OSB Sturdifloor or $20 if I get CDX plywood. For 24 linear feet I'd need 6 1x8 boards which would cost $38. So the cost is almost 2X - there's my answer. 1x8 pine board is a tad thicker but I'd assume 5/8" plywood is sufficiently strong for my needs. Can I get by with 1/2" OSB or CDX or is that going to be too bendy? Or do I need to go 3/4" OSB or ply? I'm lost on what the various "span ratings" etc mean in practice for a 180 pound person walking on a catwalk.....

2) can I get by with 30" or even 36" spacing between the 2x10 risers? I have a single 1x8 board in my garage and I stood on it last night....I weigh 180 pounds and it felt very solid with 30" spacing between blocks underneath it. I don't want to over-spec this with 2x10 pieces every foot or whatever because while that would certainly be stable and I could drive a truck on it, I'm adding extra materials cost and dead weight with each 5 pound riser that is unnecessary....

Unfortunately I prob can't finish and insulate the catwalk before the guys come because they are doing air sealing and they'll need to get at some conduit protrusions as well as some can lights and I don't want to finalize something that is then somehow in their way. I'm thinking I'll just install the risers and then they can blow the stuff around, then I'll come back and add the top deck.

the 2x10 would be side runners of undetermined length as of yet and is determined by how easily you can access the attic space with the lumber. you could start with 8' stock for the runners.The runners will go perpendicular to the joists or diagonal or parallel. The 16" or 24" spacer blocks ( depending how wide you make the walkway) are laid out at 2' or 4' centers in between the two side runners creating a ladder of sorts and you want these spacer blocks to land where the seams in the plywood are, hence the 2 or 4 foot increments. with your walkway you want to emulate how the joist system looks and is built, imagine one of the joist bays with blocks turned upright and spaced every 2' and then take that and set it up on top of the joists, that is what your walkway will look like.

For the 16" walkway you can basically build directly in line and on top of the ceiling joists that are there and once you have the ladder framed the walkway will hold its own structure, you simply need to attach a few vertical blocks ( as mentioned in other parts of this thread) to tie the ladder to the existing joists. if you build it across the joists, perpendicular or diagonal the same holds true, the ladder will hold its own structure and will only need to be tacked down to the ceiling joists.

with spacer blocks spaced 2' along the ladder 1/2" osb is plenty strong for the catwalk...

that will be fine to let them get it insulated and then you come back last and deck it.

Last edited by hand drive; 08-23-2012 at 01:24 PM.
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Old 08-23-2012, 02:48 PM   #21
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Attic catwalk design


Great - thanks. I need to get back up there tonight to have a look. In theory what you're saying makes a lot of sense but in practice it might not be that simple because I'll be spanning various HVAC ducts as well as some metal electrical conduit runs. I'm thinking it won't be as simple as just laying down my "ladder" on the floor and tacking it down. I might have to either just stand up 2x10 pieces with metal brackets or another thought just popped into my head.....making "H's" which would basically be sections of 2x10 sitting parallel on top of the joist with a 16" piece perp across the inside attaching them together........I could throw down an "H" in between each duct (the catwalk is going to be parallel to the HVAC trunk and therefore stepping over several ducts that are coming off it at 90 degree angles). Then I could tack down the OSB flooring across the Hs provided that the distance between the "runner" part of each H doesn't leave too much gap for the OSB to sag down. Maybe I'd go with a 5/8 or 3/4 OSB instead of 1/2 just to keep the sagging to a minimum. Gotta go stand on some OSB at the lumberyard to see how much it really deflects.

The benefit to doing "Hs" is then I don't rely on metal brackets to stand up the 2x10s vertically.....the H does it and I'd just need something to make sure the H can't move laterally off the joists that it's sitting on. Just angle a screw diagonally at the bottom where it sits, or do I need some bracket or side gusset?

One more question for since you're a carpenter.....I've read to use Deck Screws for something like this. If I'm working with 2x10s non-pressure-treated and OSB can I just screw them in straight or do I need to pre-drill holes? Will a pine 2x10 split from a screw without a pilot hole?

Last edited by Hogan773; 08-23-2012 at 02:52 PM.
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Old 08-23-2012, 08:41 PM   #22
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Attic catwalk design


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Originally Posted by Hogan773 View Post
Great - thanks. I need to get back up there tonight to have a look. In theory what you're saying makes a lot of sense but in practice it might not be that simple because I'll be spanning various HVAC ducts as well as some metal electrical conduit runs. I'm thinking it won't be as simple as just laying down my "ladder" on the floor and tacking it down. I might have to either just stand up 2x10 pieces with metal brackets or another thought just popped into my head.....making "H's" which would basically be sections of 2x10 sitting parallel on top of the joist with a 16" piece perp across the inside attaching them together........I could throw down an "H" in between each duct (the catwalk is going to be parallel to the HVAC trunk and therefore stepping over several ducts that are coming off it at 90 degree angles). Then I could tack down the OSB flooring across the Hs provided that the distance between the "runner" part of each H doesn't leave too much gap for the OSB to sag down. Maybe I'd go with a 5/8 or 3/4 OSB instead of 1/2 just to keep the sagging to a minimum. Gotta go stand on some OSB at the lumberyard to see how much it really deflects.

The benefit to doing "Hs" is then I don't rely on metal brackets to stand up the 2x10s vertically.....the H does it and I'd just need something to make sure the H can't move laterally off the joists that it's sitting on. Just angle a screw diagonally at the bottom where it sits, or do I need some bracket or side gusset?

One more question for since you're a carpenter.....I've read to use Deck Screws for something like this. If I'm working with 2x10s non-pressure-treated and OSB can I just screw them in straight or do I need to pre-drill holes? Will a pine 2x10 split from a screw without a pilot hole?
The H blocks are the idea and/or a full box (rectangle) might be even better to give support at the very ends. Also consider a 2x4 set flat on the top upper edges that could span the walkway across the ducting( the plywood wood go on top of the flat 2x4's). Also if the walkway is built correctly it can turn corners and even branch off, anything to fit the space. Vertical 2x4 bracing connecting walkway to joists at or near all outside corners and spaced out evenly along the longer spans would work good to hold the walkway in place.

pre drilling for screws is not necessary for framing but will help if you have a hard time at getting screws to set without camout. I recommend the deck screws that have the star drive tips( 3" for framing) , any screw length over 2" with a Phillips tip will likely strip out without predrilling. I use the star drive for any type of framing usually.
Also consider construction adhesive at the connecting points in the framing.

Last edited by hand drive; 08-23-2012 at 08:50 PM.
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Old 08-23-2012, 09:06 PM   #23
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Attic catwalk design


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The H blocks are the idea and/or a full box (rectangle) might be even better to give support at the very ends. Also consider a 2x4 set flat on the top upper edges that could span the walkway across the ducting( the plywood wood go on top of the flat 2x4's). Also if the walkway is built correctly it can turn corners and even branch off, anything to fit the space. Vertical 2x4 bracing connecting walkway to joists at or near all outside corners and spaced out evenly along the longer spans would work good to hold the walkway in place.

pre drilling for screws is not necessary for framing but will help if you have a hard time at getting screws to set without camout. I recommend the deck screws that have the star drive tips( 3" for framing) , any screw length over 2" with a Phillips tip will likely strip out without predrilling. I use the star drive for any type of framing usually.
Also consider construction adhesive at the connecting points in the framing.
Excellent thanks

I assume "construction adhesive" is something more robust than Elmers Wood Glue......probably something in caulk tube?

The funny thing is, once I complete this project I'll probably never use the walkway since I don't really store anything up there! But I think it's prudent to leave a path over to the A/C trunk area just in case I need to do more leak sealing or something. My actual HVAC unit is encased in a special room up there that is already easily accessible at the top of the stair, and there won't be cellulose right over there.

Thanks for the steer on the star drive....I never would have known to look for that.
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Old 08-23-2012, 10:01 PM   #24
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Attic catwalk design


I'm really glad to help. Yes, construction adhesive caulk may not be needed though,(your choice) if 3" screws in framing and 3"screws through the decking into the framing is used.
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Old 08-23-2012, 11:21 PM   #25
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Attic catwalk design


Uggh. I just went up to the attic again to draw and measure. There all kinds of electrical conduits going everywhere at angles, and about 2 inches above the joists. In a few places it's hard to really find a way to lay out the 2x10s. Could perhaps measure and notch them to fit over.

I'm now rationalizing that I might not really venture into this space at all except for emergencies and so why am I building the Golden Gate Bridge in one specific area of the attic? I mean I'm leaving 90% of the attic untouched yet I'm building a solid 2x10 catwalk along a single stretch? If I ever really needed to, I can step into 8 inches of cellulose or rake it aside. Wondering if maybe the lazy man's way is to cut some pieces of OSB or plywood and just tack them down on top of the rafters in the area I MIGHT walk in in said emergency, and then let them blow the cellulose on top. That would provide a safe way to step through the cellulose without trying to divine where the rafters are and should eliminate the sight of my foot sticking through the ceiling!

I dunno - think I'm probably tired so need to sleep on it and maybe I'll feel re-energized for the original challenge tomorrow.

Anyway, thanks again for all the helpful advice. In any case I'll be up there tomorrow with some mastic and foil tape to address a few leaks I found along the trunk where the ducts attach. Fun stuff!
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Old 08-24-2012, 10:51 AM   #26
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Attic catwalk design


Hogan773 I wouldn't step through the cellulose onto OSB on the joists. The cellulose will be compacted and lose insulating value. Similar thing happened in my old house, 12" of fiberglass and 2x6 joists. There was a trail running the length of the attic where everyone walked and the 'glass was visibly compressed and less efficient.

I'm in the same boat as you now BTW. However I only need to add 6" of insulation to my new house, and my catwalk would go perpendicular to the joists. I was thinking of standing up a 2x6 and using hurricane ties to attach it to the joists, but after looking at tony.g's drawing I could stabilize the 2x6 with 2x2 "posts" cheaper (the ties are 40 to 80 cents a pop).

Once I have the 2x6 secured, I'll just nail a 2x4 flat across the top of that for a walking surface. Maybe a 2x6 if I want luxury. Hey this is a catwalk, not an interstate freeway.

I'm sure I'll have to notch for wires and such, probably just take a recip saw or rotozip with me to the attic and hack where necessary without measuring. It won't look pretty, but the new insulation will hide that.
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Old 08-24-2012, 12:06 PM   #27
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Yeah I hear you.....like I said it was late and I was tired and thinking "why am I really going to go buy lumber, screws etc and build this thing when I probably won't walk up in the attic in the next 5 years. As my furnace is already accessible and will remain so, the only reason I'd be going elsewhere is to check the HVAC trunk for air leaks (which I'll be doing now before the insulation) or if there is an emergency like a roof leak or something.

I thought that I COULD step through cellulose and/or sort of rake it to the side a little, and for $5.99 a bag if I was really concerned I could carry a bag up there and dump more in if it is "compressed" at some point in the future. One $5.99 bag claims to cover 40 sqft to R-19 depth.

Trip to Menards later today and I'll see what I end up buying there! Maybe I'll just stand up a few 2x10s in clean spots and then lay a 2x6 or 2x8 across the span and just bridge over all the conduit and ducts. I need to see how strong a 2x8 is when I go to the store but I'm guessing that I could easily span 4 or 5 feet sections if I needed to and not have it flex excessively on my 180 pound weight. Again, just for emergencies.

The reason I was hesitating is because I am not going to build a full catwalk across the whole attic floor that gets me everywhere I'd ever need to conceivably go, so I questioned the value of building a Golden Gate Bridge catwalk in one specific section......just figured it might be slightly more likely I'd want to access the HVAC distribution trunk at some point, but I don't know whether that is once every 2 years or once every 5.

Now onto another question.....bathroom vents exhausting to the roof. I may post that elsewhere if this isn't the right forum.
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Old 08-24-2012, 12:30 PM   #28
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Trip to Menards later today and I'll see what I end up buying there! Maybe I'll just stand up a few 2x10s in clean spots and then lay a 2x6 or 2x8 across the span and just bridge over all the conduit and ducts. I need to see how strong a 2x8 is when I go to the store but I'm guessing that I could easily span 4 or 5 feet sections if I needed to and not have it flex excessively on my 180 pound weight.
I have a 2x12, 8ft long, that I use as a motorcycle ramp. A 400lb motorcycle with about 200lb on each tire, it sags a little but not a scary sag by any means. I'm sure an engineer would shudder at the thought but I wouldn't be too worried about a 2x8 placed flat and supported at 4ft intervals holding up a 180lb guy, the weakness is in the joints and fasteners. As you step mid-span, the 2x8 will bow and pull the supports toward you under bending stress. Ensure the supports are reinforced against bending and you should be good.

Note, I am not an engineer...
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Old 08-24-2012, 12:47 PM   #29
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Attic catwalk design


Yeah I have a 1x10 pine board that is my "helper" in certain situations......I've used it to slide a 200 lb generator in shipping crate out the back of my minivan and down to the ground....just slide down the board.

My guess is I could probably stand in the middle of an 8 foot span of 2x8 with no intermediate piers and it would still be fine......obviously the more piers the better though to distribute weight and reduce bending, as you said. And no I'm not an engineer either! (as if that wasn't already obvious)
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Old 08-24-2012, 03:29 PM   #30
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My guess is I could probably stand in the middle of an 8 foot span of 2x8 with no intermediate piers and it would still be fine....
In theory, it wouldn't work. A 180lbs weight in the middle of a 2x8 (probably actually 1.5" x 7.5") would produce a bending stress of about 1500lbs/sq.in. Most commerciially available softwoods have a max. permissible stress of 800- 1200 lbs/sq.in.
So while in theory it would snap, here on planet earth it won't because of the safety factors built-in to the figures. (it would bend a lot, though!).
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