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Old 08-22-2012, 04:58 PM   #1
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Attic catwalk design


Hi all - I'm a new poster here.

I am about to get cellulose and air sealing in the attic. I'd like to build a simple catwalk that would allow me to get access to the side of the HVAC trunk system in case I need to access it to check for leaks etc in the future. I want to do this before the floor gets 8-ish inches of cellulose.

I have 2x6 rafters on 16 inch spacing in the attic now, with R-19 batts stuffed in between.

I was originally thinking a simple design with some 2x6 pieces, stood upward (so 5" height) and laid across 2 rafters perpendicular, then a plywood deck on top. But 2 problems....1) this only gives me 5 extra inches and I really need 8+. Second problem is there are sections of conduit, the HVAC supply and return ducts, etc all around too, so it makes it more challenging to get clean even spacing.

Now I'm thinking about cutting 8 or 10 inch lengths of 2x4, standing them up on the 2x6 rafter, attaching them to same so they make "posts" and then running horizontal 2x2s or 2x4s to make a "top rail" that sits on those posts, and then throwing a plywood deck on top to walk on.

Questions for the experts on here

1) are there problems with my design? I realize that by standing up 2x4s I'll be loading the rafter but I figure that the existing rafters have already been holding my 180 pound weight directly as I've been walking on them, and the "rail" connecting along the tops would act as a beam and distribute the weight among several 2x4 posts.

2) What is the best method to "stand" the 2x4s up on the 2x6 horizontal chords? Should I use a metal L-brackets at the corner between them, or some sort straight metal bracket down the side that screws into the side of the 2x6 and the 2x4? Or a plywood gusset on one side? I'm trying to envision whether there are risks that the standing 2x4 post "slips off" the 2x6 it's sitting on one side or the other, or whether I should be worried about the 2x4 rotating and falling down. I'd think when the top rail is attached the risk of any single post rotating forward is small, but one would want to make sure that the whole thing wasn't able to shift sideways so that it "falls off the rails" and into my ceiling.

Or would it be better to take 16" sections of 2x4 and attach them across the posts to make "arches" and then lay a 1x10 board down the middle of those arches? I don't really need 16 inches width of catwalk I guess. How far could I get the spacing of those arches....24".....30"?

I realize that I'm trying to articulate what is in my head so it might not be clear.....

any advice from you guys would be appreciated - thanks

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Last edited by Hogan773; 08-22-2012 at 05:32 PM.
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Old 08-22-2012, 05:25 PM   #2
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Attic catwalk design


why not run 2x6 joists on top of existing joists, perpendicular to the existing ceiling/attic joists at 12" to 16" o.c. and put your decking on top of that. It would provide you with about 11" of insulation and would be more stable that a bunch of "posts".

of course you would first need to do an analysis to determine if the existing 2x6 joists could support the imposed loads of someone walking around. your post does not indicate the spans of the joists. check out this link from the 2009 International Residential Code (basis for most building codes in United States) for spans of ceiling/attic joists.

http://publicecodes.cyberregs.com/ic...9_5_par020.htm

your existing ceiling/attic floor system may not have been designed for people to be up there, plus do not know where your load being walls are below (if any) in relationship to your walkway. If the existing joists cannot handle the load you'll be looking at cracks in your ceiling (at minimum).

just my humble ramblings ....

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Last edited by GBrackins; 08-22-2012 at 05:28 PM.
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Old 08-22-2012, 05:46 PM   #3
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Attic catwalk design


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Originally Posted by GBrackins View Post
why not run 2x6 joists on top of existing joists, perpendicular to the existing ceiling/attic joists at 12" to 16" o.c. and put your decking on top of that. It would provide you with about 11" of insulation and would be more stable that a bunch of "posts".

of course you would first need to do an analysis to determine if the existing 2x6 joists could support the imposed loads of someone walking around. your post does not indicate the spans of the joists. check out this link from the 2009 International Residential Code (basis for most building codes in United States) for spans of ceiling/attic joists.

http://publicecodes.cyberregs.com/ic...9_5_par020.htm

your existing ceiling/attic floor system may not have been designed for people to be up there, plus do not know where your load being walls are below (if any) in relationship to your walkway. If the existing joists cannot handle the load you'll be looking at cracks in your ceiling (at minimum).

just my humble ramblings ....

Thanks for the input....I realize my original post was long and convoluted but basically your idea was my first idea but I scrapped it because it won't be high enough AND the location of various conduits and ducts makes it harder to get nice even spacing across the existing joists.

They are planning to add 8 inches of cellulose and the current fiberglass is even with or extends above the existing 2x6 joists, so putting another 2x6 perpendicular just adds 5 inches of new space. It will be buried when they're finished blowing.

I agree re: existing loading but I have been in the attic many times before, as have some others, walking carefully along the 2x6s and they've held fine. I'm not planning on storing anything on this catwalk.....just walking.
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Old 08-22-2012, 05:57 PM   #4
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Attic catwalk design


Not sure how old your duct work is but if it was me I’d be spending “cat walk funds” on inspecting, repairing or updating the ducts (or anything else) before it all gets buried.
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Old 08-22-2012, 06:11 PM   #5
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Attic catwalk design


use a 2x8 with 3/4" plywood sheathing ..... 7-1/4" + 3/4" = 8"

or stick with the 2x6 with 3/4" = 5 1/4" + 3/4" = 6" and tell them not to cover the walkway
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Old 08-22-2012, 06:14 PM   #6
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Not sure how old your duct work is but if it was me I’d be spending “cat walk funds” on inspecting, repairing or updating the ducts (or anything else) before it all gets buried.
I agree .....

make sure to insulate the ductwork with R-8 insulation minimum (check with your local codes, could require more) and make sure they are sealed. don't want leakage into a "cold" space. creates all kinds of issues
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Old 08-22-2012, 07:16 PM   #7
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Attic catwalk design


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Not sure how old your duct work is but if it was me I’d be spending “cat walk funds” on inspecting, repairing or updating the ducts (or anything else) before it all gets buried.
I already checked myself and there are just a couple noticeable leaks. One is where a duct came apart from the trunk and is about 1/2 inch. A few others are small. I'm going to go up this weekend with some mastic and tape and play.


The contractor will be doing air sealing so they'll be boxing can lights, foaming cracks, etc before blowing.

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Originally Posted by GBrackins View Post
I agree .....

make sure to insulate the ductwork with R-8 insulation minimum (check with your local codes, could require more) and make sure they are sealed. don't want leakage into a "cold" space. creates all kinds of issues
My home was built in 2004 and all the ducts are already wrapped tight with R 4.2. Beyond fixing obvious leaks, I'm not sure how practical it is to re-wrap or over-wrap all the ducts to get to R-8. (Is R-8 even the requirement?) At Menards and HD here they sell 6.9 duct wrap.

I can seal some leaks myself but it doesn't seem worth it to pay an HVAC contractor $1000 or more to add R-3 or 4 to my ductwork.....there are quite a few ducts. Most of the ductwork will be mostly or fully covered in cellulose too at the end of this job which will add to their R-value I'd think. Just the main trunk will be above. I wonder if there is an easy way for me to wrap some new insulation around the trunk only....maybe just laying pieces of foil pipe wrap across and foil taping on top of the existing foil wrap that covers it now. I guess even if I get 85% of it wrapped up with another layer, that would make it better, no?

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Old 08-22-2012, 08:39 PM   #8
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Attic catwalk design


My comment on R-8 insulation for ducts is based upon the 2009 International Energy Conservation Code by the International Code Council, your code may differ. Check out this link for their requirements

http://publicecodes.cyberregs.com/ic...9_4_sec003.htm

Just make sure you use HVAC tape (metal foil) not duct tape ...... any reduction in leakage and increase in insulation is a good thing

Good luck!
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Old 08-22-2012, 10:17 PM   #9
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Attic catwalk design


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My comment on R-8 insulation for ducts is based upon the 2009 International Energy Conservation Code by the International Code Council, your code may differ. Check out this link for their requirements

http://publicecodes.cyberregs.com/ic...9_4_sec003.htm

Just make sure you use HVAC tape (metal foil) not duct tape ...... any reduction in leakage and increase in insulation is a good thing

Good luck!

Thanks. My question on the duct insulation is - when the A/C was running full bore if I place my hand on the top of the insulation, I don't feel any "cold" sensation. Therefore is there really a benefit to adding another layer of foil insulation on top if I am just going to be insulating something that isn't cold as it is? (I mean the cool temperature of the duct is staying inside the current insulation)

EDIT: I googled and came up with this http://ducts.lbl.gov/distribution.html#insulation

While I can't view the graph on PC, the text basically says that there are fast diminishing returns to higher amounts of duct insulation.

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Old 08-23-2012, 12:10 AM   #10
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Attic catwalk design


I couldn't tell you if you'd save money or not by installing more insulation around the ducts or not. I'd spend my time and efforts in sealing them so there are no leaks and see what happens

I was just stating where my R-8 suggestion came from ..... here we don't have any choice, if your ducts are outside of conditioned space they must be insulated to a minimum of R-8.

Good luck!
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Old 08-23-2012, 12:46 AM   #11
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Attic catwalk design


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I couldn't tell you if you'd save money or not by installing more insulation around the ducts or not. I'd spend my time and efforts in sealing them so there are no leaks and see what happens

I was just stating where my R-8 suggestion came from ..... here we don't have any choice, if your ducts are outside of conditioned space they must be insulated to a minimum of R-8.

Good luck!
Thanks....I wish I had R-8 but the code must have been different when my home was built. That was only 8 yrs ago....I guess things change quickly!

Much of the runs will be sitting in cellulose so I'll certainly get some extra kick there. I'll just focus on the leaks at the trunk since I can't really feel any leaks along the runs, and they're all sealed up with continuous insulation wrap (one piece). There also some spots where there is just foil tape at the junction of the trunk and the duct...ie the foil tape is taping the insulation down on the metal duct and where the foil is the only thing on the duct metal, if you put your hand on it it is cold. So I may try to wrap some extra material around those unions to avoid thermal losses there. Probably not nearly as bad as an actual air leak in terms of performance though, I am assuming.
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Old 08-23-2012, 12:52 AM   #12
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Attic catwalk design


With R-8, you would be losing about 10% of the heat/cold air to the attic. If the main trunk is surrounded/under the cellulose by 50%, about 5% loss; pp.2, convert from R-3.6 per inch; http://www.enersavesystems.com/pdf/E...Insulation.pdf

Add plywood sides around the trunk for complete coverage of cellulose. Be careful not to exceed the weight limit of the drywall; http://www.energyguide.com/library/E...SubjectID=8375

Check locally, some HVAC catwalks require 16-24". Keep in mind it should be plywood, not OSB (molds easier) in my opinion. Drill 2" air holes @ 6" to vent the cellulose to the attic air. The fiberglass will be compressed 1-2" by the cellulose, increasing it's density for a higher R-value per inch. Add solid blocking between the new joists every 5-6' and the joints/ends to prevent rotation. Leave the top off for insulation install, have them lay them in place loosely (to walk on) as they back out while applying. Screw the new joists to every old joist, perpendicular and centered over a bearing wall. If possible, wire some new lighting up there beforehand to get a premium job. Vacuum the existing loose-fill from the soffits before they add plastic baffles (with a wind-washing protection over the exterior wall) to reach 12" above the new blow-in, which also keep the soffit empty of insulation; http://www.bergerbuildingproducts.co...sAccuvent.html

http://www.owenscorning.com/around/v...s/VentSure.pdf

Gary
P.S. where are you located, we can figure your insulation needs....
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Old 08-23-2012, 01:39 AM   #13
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With R-8, you would be losing about 10% of the heat/cold air to the attic. If the main trunk is surrounded/under the cellulose by 50%, about 5% loss; pp.2, convert from R-3.6 per inch; http://www.enersavesystems.com/pdf/E...Insulation.pdf

Add plywood sides around the trunk for complete coverage of cellulose. Be careful not to exceed the weight limit of the drywall; http://www.energyguide.com/library/E...SubjectID=8375

Check locally, some HVAC catwalks require 16-24". Keep in mind it should be plywood, not OSB (molds easier) in my opinion. Drill 2" air holes @ 6" to vent the cellulose to the attic air. The fiberglass will be compressed 1-2" by the cellulose, increasing it's density for a higher R-value per inch. Add solid blocking between the new joists every 5-6' and the joints/ends to prevent rotation. Leave the top off for insulation install, have them lay them in place loosely (to walk on) as they back out while applying. Screw the new joists to every old joist, perpendicular and centered over a bearing wall. If possible, wire some new lighting up there beforehand to get a premium job. Vacuum the existing loose-fill from the soffits before they add plastic baffles (with a wind-washing protection over the exterior wall) to reach 12" above the new blow-in, which also keep the soffit empty of insulation; http://www.bergerbuildingproducts.co...sAccuvent.html

http://www.owenscorning.com/around/v...s/VentSure.pdf

Gary
P.S. where are you located, we can figure your insulation needs....

Wow - thanks for all that good info.

My supply trunk is on the bottom and the return trunk is directly on top. This should be a good thing as it makes it easier to "bury" the supply side under the cellulose, and the return trunk sort of insulates it from the top.

Not sure how I'm gonna build a plywood box since there are 4 ducts coming off one side and several on the other....I'll ask the contractors what they can do.

I've already got 2 light sockets up there so I'm probably OK there.

When you say I might need 16" or 24" what do you mean....width I assume? Or distance between my new joists/arches?

Is there really a code for attic catwalks when nobody can stop me from tiptoeing down the joists as I do currently? I mean there probably is a code for everything...I'm just wondering when something like an attic catwalk would be enforced in reality. Probably only if/when we sold the house I'd think.

Can you envision my "arches" plan to support the catwalk and does it make sense? I'm thinking of standing 8 or 10 inch lengths of 2x4 on end, attaching them to the top of the existing joist with an angle bracket, then putting a 2x4 across the top perpendicular to the existing joists. Basically a variation on the idea others mentioned about just laying down 2x6s across the joists, but would allow me to build HIGHER without the added weight of trying to stand up 2x8s or 2x10s which are heavy. It only needs to hold my weight and I'd think a 2x4 "arch" spanning only 16 inches should not have any issue with normal human's weight, especially because the plank above would beam the weight across multiple arches.. I am thinking the angle brackets should help avoid any tendancy for the posts to move side to side or fore and aft. I might be crazy though. My guess is it will work fine, but I'm wondering if the engineers out there would tell me I'm not doing it correctly.

Thanks to this thread I'm getting some good ideas. I never really thought about burying the trunk in cellulose until this thread....
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Old 08-23-2012, 07:40 AM   #14
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Old 08-23-2012, 08:49 AM   #15
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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.

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