Insulation project and weight concerns in attic

[DavidV]

I have a walk up attic. Very very poorly insulated with the pink blow in stuff .I currently have some OSB panels up there laid across the joists as a place to store stuff. I want to increase the insulation up there and not lose my storage. I plan to pull up the osb, add a framework of 2x6 lumber that runs across the joists at a 90 degree angle. Put in celulose insulation and then put down 1/2 or 3/4 inch plywood. I wopuld then build some Shelves above that so that I could walk down the middle of the attic and have organized storage of all our crap . Currently it's just a bunch of haphazard stuff up there. I am wondering about the increased weight of the framework and if that is something I should be concerned about. House was built in 1987. I am thinking that metal storage shelf systems might shave some weigtht from up there. I am open to any ideas of how to accomplish the insulation increase and minimize the weight load I put on house.

Thanks.

 

[Sandor]

David,

Why run 90 degrees? It will change the load characteristics of the floor, don't do it. If you do not want to tear up the floor, simply make multiple lenghtwise cuts to the existing floor (for ventilation), lay your 2x6 directly over the floor joist and make sure the ends go to the outside walls of the home, or over a load bearing interior wall. This will maintain loading, as it was designed. Insulate in between your new 2x6's, then lay the new floor.

Do the same thing if you want to remove the floor and reuse it. Just make sure the 2x6 are directly over the current floor joists/rafters. Add bracing between the 2x6's (perpendicular) so they will not roll.

Put your shelves over the outer most part possible, or interior is fine as long as its over a load bearing interior wall.

Post pics if you need more clarification.

 

[Rhone]

Well, if you do live in Richmond I see it recommended you insulate to R49. They recommend I insulate to R60, but when I'm done I'll have a woeful R49. So, I went and calculated how many btu's I'd save going R60 instead of R49 over a winter. It came out to 9 gallons of oil/year. NOT worth it.

If you want to know how many btu's you'll save by insulating here are the results using the heating & cooling degree days for Richmond VA, with an attic that's 1400 sq. ft. I'm assuming yours is around that give or take. BTW your attic insulation I currently estimate it to be R13.

Going from
R13 to R30 by adding 5.5" cellulose insulation & 2x6's = savings of 5,739,828 btu's/year heating and 2,147,126 btu's/year cooling
R13 to R36 by adding 7.5" cellulose insulation & 2x8's = savings of 6,471,374 btu's/year heating and 2,420,780 btu's/year cooling
R13 to R49 by adding 11" cellulose insulation = savings of 7,441,793 btu's/year heating and 2,783,789 btu's/year cooling

Well, this was a bit of an upset for Richmond VA. I was hoping to show you that you should at least go to 7.5" of cellulose but at a savings of only 732,000 btu's of heating and 300,000 btu's of cooling, NOT going to be worth and neither is your states recommended levels. So, good choice on the 5.5" of cellulose. Wow, choosing to go 7.5" cellulose instead of 5.5" would take you 20 years before you saved yourself a cord of wood, and save you a whopping 6.5 gallons of oil per year.

Okay, 5.5" is a great idea for insulation. My recommendation is to rip out the OSB as Dylan suggested and this is the most important piece of information I can give you. Either, you attach the shelves so they hang from your rafters OR attach them to the floor but NOT both. I can't say which you should do. But, in my house, the previous owners did such. They attached 2x6's from the center of the rafters to the center of the ceiling joists below. They then put another layer of asphalt shingles on the roof and you know those things weigh a ton. Then, a huge snow storm came. The rafters with huge amounts of snow and 2 layers of shingles sagged a couple inches under the weight and since these 2x6's directly connected them to the ceiling rafters below THE CEILING SAGGED 2" also! It cracked and bowed and never sprung back. After buying the house, last year I set up supports in the basement, then into the living room, removed the 2x6's they had connecting the centers of the rafters to the ceiling joists, and with a car jack slowly cranked the ceiling back up beyond the 2" and then fastened them directly to the ridge itself. That has made a world of difference. So, my point is 5.5" cellulose is a good choice, and either fasten the shelves to the rafters/ridge or to the floor, not both and allow a couple inches for movement if you get a big snow load or such.

 

[Sandor]

As Rhone found out, and I stated above, the 2x6 must extend to a load support point on the outside wall, or inside load bearing wall.

You can't just raise the inner part of the floor with the 2x6 without hitting an underlying support, and just letting the truss or joist hold the load.

I also assumed you were not storing boxes of gold bullion up there either.

Hey Rhone, you a math guy or what!?!?!?! And, I hope you added collar ties when you supported the joists to the ridge.

 

[elkimmeg]

Floor loads are tupically 40 to 50lbs per sq ft Ceilings 15 to 20 per sq ft including the weight of the joist and plaster
As Sandor said follow your existing ceiling joist nail a few strapping strips or blocks to hold them in place and prevent rolling and add your insulation shelving and osb plywood. Insulation to a point, factor bang for buck, just like memory 128 to 512 is your best preformance gain over that the increase gains diminishes.

 

[HarryBack]

ok,ok, sure....splitting hairs.....are you sure your basement carrying beams and any large headers are sized adequately for 3 full floors of weight? And Id be VERY surprised to see 2x10's there in the attic...my money is on 2x8's...or even worse *gasp*....2x6's.

And, Lord help us, DO NOT ATTACH ANYTHING TO YOUR RIDGE OR RAFTERS! They most likely barely meet code, and unless the ridge has been designed and engineered to act as a structural ridge (and if its just a 2x10 or 2x12 it HASNT been), DO NOT attatch ANYTHING to the ridge! If the rafters are attatched to the cieling joists with supports or ties, some of your roof load and delfection will be transferred to your cieling. The allowable deflection for a rafter or beam is greater than the allowable deflection for a cieling joist. In other words, the plaster or drywall will crack if you go over the allowable deflection for the cieling, which you very well may do if you load your cieling joists with roof load which isnt factored in in most loead tables.

 

[Sandor]

ok,ok, sure....splitting hairs.....are you sure your basement carrying beams and any large headers are sized adequately for 3 full floors of weight? And Id be VERY surprised to see 2x10's there in the attic...my money is on 2x8's...or even worse *gasp*....2x6's.

And, Lord help us, DO NOT ATTACH ANYTHING TO YOUR RIDGE OR RAFTERS! They most likely barely meet code, and unless the ridge has been designed and engineered to act as a structural ridge (and if its just a 2x10 or 2x12 it HASNT been), DO NOT attatch ANYTHING to the ridge! If the rafters are attatched to the cieling joists with supports or ties, some of your roof load and delfection will be transferred to your cieling. The allowable deflection for a rafter or beam is greater than the allowable deflection for a cieling joist. In other words, the plaster or drywall will crack if you go over the allowable deflection for the cieling, which you very well may do if you load your cieling joists with roof load which isnt factored in in most loead tables.

Harry, I have seen many engineered attic trusses, 24 feet and less, with a 2x6 bottom chord.

 

[DavidV]

Ok. 2x6's . Walk up attic. So I should not criss cross over the existing supports?? I would have thought that this would have distributed the load more evenly. Can I use a "header" to attatch the end of all the 2x6's I'm putting up there together, to give them more stability? How the heck do I keep the things from rolling? I'm planning on doing this in stages. One side above the master bedroom I will be doing this weekend, and then in the beginning of next week (While my entire HVAC system is replace at an ungodly cost of 6 grand) I will be doing the rest of it. There is a crawlspace not a basement. I have NO intention of attatching anything to the roof. I appreciate all the advice. The reason for not reusing the OSB is I frickin hate OSB. it sags and I always feel like I'm about to go right thru it when I step on it. I'm wondering if 1/2 inch plywood will be adequate to support my weight. I'm not gonna be up there all that much, just gonna create an alley with shelves on either side so I can put all the seasonal decorations and boxes of heriloom crap that goes to the kids. pictures, yearbooks, all that foolishness. most of it doesn't weight too much but it takes up a huge amount of space up there. I'm looking into light weight plastic shelving that is supposed to hold 750 lbs. I want to minimize the added weight.

 

[elkimmeg]

I could get out the code book and check design loads for Ceiling joist vs spands
but 20 steps back let's try to keep it simple. If one could center the additional weight over the carring wall
then chances are it would handle the additionnal storage weight with out a lot to do. If the storage is heavy,
and text books can be, and approaching the mid spand of the ceiling joist additional support is needed.

Without code lessons here a balance l load of 3' each side of the bearing wall, should work without muct to do
So cut 6' 2/6 toenail then to your existing joist and I like your end box idea again toe nailed into the existing joist.
then insulate
OSB/ vs 1/2" plywood. Plywood is rated 16/32 approved for normal floor load 16' on center 32" side wall 16/32 stamp

Personally I think you will feel the same way as you do with the OSB like you could go threw it. 5/8" is the way to go for walking
1/2 can be used for shelving

 

[DavidV]

Renting a storage bin is out. One of the reasons I bought the place was walk up attic. taking away 6 inches of attic would still provide enough for storage. With only 5.5 inches of pink stuff up there I feel I really must double my depth with some cellulose insulation. I have to ask the question about crossing the current joists. How would this be much different than the having osb or plywood spread across them to distribute the load like it is right now. Currently there is about 800 SF of osb and plywood up there with assorted stuff on it.
supports on one end of the attic run side to side (of the house ) and on the other side of the stairs they run front to back of house. .

 

[DavidV]

Basicly the only change to the attic situation from what we have right now is that It would be organized, insulated and there would be the additional framework of 2x6's. Not planning to add much to what's up there. in fact we will likely get rid of a lot of it as we go thru it.

 

[Rhone]

HarryBack has really nailed the point. 2x6's can't handle a lot of weight, at all. My 2x6 rafters were sagging around 3" when I bought my house so they were undersized. I checked today what sized rafters would be required for my area with my layout and mine needs 2x12's. Okay, maybe that's why my roof sagged so much. Being so much work to sister rafters especially since I'm choosing to sister full length, do I just put 2x6's with my current 2x6's and get the strength of a 2x12? I went to the span calculator from the forestry website and found something very interesting. That is, a 17' 2x6 could hold 714 load and 2x8=1,445 and 2x10=2,329 and 2x12=3,128. Wow, had I sistered my current 2x6's with another 2x6 my rafters wouldn't even be the strength of a single 2x8 let alone a 2x12. A 2x12 is around 4.5x stronger than a 2x6! So, I sistered my current 2x6 rafters with 2x10's so they can handle a combined load of 3,043 which is close enough to a 2x12's 3,128.

Point being your current 2x6 ceiling is really weak like HarryBack warns, and woods strength comes from its thickness. If you can put like people are saying, your 2x6 exactly on top of your current 2x6 and go as close as you can to the soffits and as close as you can to a support wall that will help your floor be stronger and spread the weight over the entire beam, and less chance of sagging the ceiling. I don't think it will be as strong as a 2x12, but stronger than if you do like you were planning and criss-cross your 2x6's. I don't know the physics behind it, but stacking the two on top of each other to look like a 2x12 there's two pieces of wood over or extremely close to support members, so they both can share and support more weight whereas criss-crossing has only one 2x6 near suppport members the entire length, and will have to carry all the weight, of which they can't carry much without sagging. I think you can use metal truss plates to hold the 2x6's on top of the other 2x6's, they're very inexpensive at Home Depot and Lowes. Here's a picture of one (broken link removed), they also have a ton of plates and fasteners like it, you may be able to find ones that are more applicable. I'd probably use some simple cross members here and there to your current ceiling joists to help stabilize. I'm not a carpenter, so if a carpenter or someone who knows carpentry has a better idea, follow their lead!

 

[Rhone]

Yeah Dylan, like Harryback was saying. It's a matter of material, use, and how much "sag" you're willing to accept given a certain load over a span. It's amazing how much wood can hold for weight before it will actually break. They'll normally just sag more and keep taking the load. You make a point that I didn't mention I was referring to deflection in my numbers, not strength before wood will actually fail. In my area, code wants 2x12's for my rafters. I went a step further and wanted to make sure my roof wouldn't sag more than a 1/2" under full load to help my skylights I'll be putting in from possibly leaking. So, the numbers in my post is not when wood fails rather how much weight spread evenly over 17' when it reaches a point it will sag 1/2". I'm pretty sure I did it for 1/2", I have all the info except that. Anyway, a 17' 2x6 will sag 1/2" trying to hold up 714 lbs spread evenly, whereas a 2x8 can hold 1,445 lbs spread evenly before it sags 1/2". I found, with 2 layers of asphalt shingles and a good sized snow load, I needed 2x12's to make my roof not sag more than 1/2".

 

[Rhone]

I think we're hijacking DavidV's post.

The front of my house's roof sagged 3-4" and the back sagged only 2". I built temporary support walls that went from my attic to the foundation directly under the sag on the front and made sure everything lined up perfectly and marked on the ceiling joists in the attic EXACTLY where my support wall lay underneath. From that I used a 5lb hammer and 3' 2x4's and hit by hit hammered them into the 2' 8" sag space between my ceiling joists and rafters. As you can see, the only way to fit 3' piece of wood into 2' 8" of space something had to give and since the ceiling joists were now supported below by my temporary support wall all the way to the foundation, the only thing that could give was the sag in the rafters. I slowly gave each 2x4 a pop going down the line and with each pop the sag would come out a little more. When I finished fitting my 3' wood pieces in the sag, the roof was perfect. I let it sit there for several months. I sistered with 2x12's in the front instead of 2x10's to compensate for the 2x6 rafters wanting to go back to their sagging state and no longer contributing support. They're basically just holding the 2x12's in place.

The back, no one can see and only 2" sag I just put a lever near the soffits over the outside walls and give it a gentle push and then sister in the 2x10 rafters. That removes about 1/2" - 1" of the sag and it gets locked having a little sag. Fine by me, no one can see my roof in the back anyhow the way my house is on the side of a hill.

 

[HarryBack]

ok,ok, sure....splitting hairs.....are you sure your basement carrying beams and any large headers are sized adequately for 3 full floors of weight? And Id be VERY surprised to see 2x10's there in the attic...my money is on 2x8's...or even worse *gasp*....2x6's.

And, Lord help us, DO NOT ATTACH ANYTHING TO YOUR RIDGE OR RAFTERS! They most likely barely meet code, and unless the ridge has been designed and engineered to act as a structural ridge (and if its just a 2x10 or 2x12 it HASNT been), DO NOT attatch ANYTHING to the ridge! If the rafters are attatched to the cieling joists with supports or ties, some of your roof load and delfection will be transferred to your cieling. The allowable deflection for a rafter or beam is greater than the allowable deflection for a cieling joist. In other words, the plaster or drywall will crack if you go over the allowable deflection for the cieling, which you very well may do if you load your cieling joists with roof load which isnt factored in in most loead tables.

Harry, I have seen many engineered attic trusses, 24 feet and less, with a 2x6 bottom chord.

Im sure you have.....they werent attic trusses tho, were they? They werent engineered to have ANY load at all in the "attic" space. An attic truss is a specific truss engineered to carry a load in the attic space. Actually creating any load space above the bottom chord in a truss not designed to do so will invariably create bad deflection at a minimum, and shear in the worst case

 

[Sandor]

They were attic trusses. It depends on the "size" of the attic space and load. This load rating was 20 lb/ft.

 

[HarryBack]

also, trusses are manufactured with MSR lumber...thats machine stress-rated lumber....each piece has been graded and tested to meet certain design criterion....this holds true in trusses anyways for the top and bottom chords, whereas, the interstitial chords can be regular SPF. You wont find MSR lumber in most lumberyards, by the way. And its critical when designing a floor/roof system that you take into account the species of lumber and its grade, in determining maximum spans.

 

[Sandor]

Renting a storage bin is out. One of the reasons I bought the place was walk up attic. taking away 6 inches of attic would still provide enough for storage. With only 5.5 inches of pink stuff up there I feel I really must double my depth with some cellulose insulation. I have to ask the question about crossing the current joists. How would this be much different than the having osb or plywood spread across them to distribute the load like it is right now. Currently there is about 800 SF of osb and plywood up there with assorted stuff on it.
supports on one end of the attic run side to side (of the house ) and on the other side of the stairs they run front to back of house. .

The crisscross issue.

When you load stuff up there or walk on the floor, those loads are transfered to a bearing support point.

When you crisscross, without going all the way to the bearing point, the load is carried by the span.

 

[HarryBack]

They were attic trusses. It depends on the "size" of the attic space and load. This load rating was 20 lb/ft.

well, I dont have the advantage of knowing where you are......BUT...here in MA, and Elk, correct me if Im wrong, any WALKUP space, not on the first floor, has to be designed to 30 lb/sq-ft LIVE load and 10 lb/sq-ft DEAD load...thats 40 lb/sq-ft TOTAL load. The first floor has a 50 lb/sq-ft Total load in most cases....outside decks? 60 lb/sq-ft. Walkup space would also be an attic truss. You might be speaking of a STORAGE truss, but thats a different animal altogether.

 

[Sandor]

also, trusses are manufactured with MSR lumber...thats machine stress-rated lumber....each piece has been graded and tested to meet certain design criterion....this holds true in trusses anyways for the top and bottom chords, whereas, the interstitial chords can be regular SPF. You wont find MSR lumber in most lumberyards, by the way. And its critical when designing a floor/roof system that you take into account the species of lumber and its grade, in determining maximum spans.

Harry, when I order trusses, I specify the dimensions, load bearing walls, the pitch, and whether I want an attic truss or not. What I get is what the firm has engineered. I trust they know what they are doing, since if they didn't, I assume they would have been sued to oblivion before they had a chance to sell me anything.

 

[Sandor]

They were attic trusses. It depends on the "size" of the attic space and load. This load rating was 20 lb/ft.

well, I dont have the advantage of knowing where you are......BUT...here in MA, and Elk, correct me if Im wrong, any WALKUP space, not on the first floor, has to be designed to 30 lb/sq-ft LIVE load and 10 lb/sq-ft DEAD load...thats 40 lb/sq-ft TOTAL load. The first floor has a 50 lb/sq-ft Total load in most cases....outside decks? 60 lb/sq-ft. Walkup space would also be an attic truss. You might be speaking of a STORAGE truss, but thats a different animal altogether.

u r correct. Sorry for the confusion. These are typical for over 24' wide garages with a 6/12 pitch. Not enough room to stand, but enough room to plunk stuff.

 

[HarryBack]

so, basically, youve got a room with a 20 lb/sq-ft loading? And I apologize...didnt see the Virginia in your post......a 20 lb/sq-ft (and Ill assume its LIVE load, not Total Load)........well, I guess Ill have to concede that codes differ with locale, and given, Virginia isnt really noted for its snow loads.....

 

[HarryBack]

LOL- our replies are criss-crossing! Ok...enough from me, Im hijacking this thread!

 

[Sandor]

so, basically, youve got a room with a 20 lb/sq-ft loading? And I apologize...didnt see the Virginia in your post......a 20 lb/sq-ft (and Ill assume its LIVE load, not Total Load)........well, I guess Ill have to concede that codes differ with locale, and given, Virginia isnt really noted for its snow loads.....

It is live load. They allow the provision, because the ceiling height is deemed not livable. Our annual snowfall is maybe a 15 inches a year. (No Grand pianos up there)

 

[elkimmeg]

whow do I sit back and observe? so much correct info where do I start? Common construction grade
lumber #1 /#2 mixed spruce or do we debate Hem fir? then there is the deffinition of walk up attic?
actual stairway not a pull down?
Warren are you confused enough? thread got hyjacked? Ask a simple question btw what was the original question?
Trusses cords ? design loades species stress factors? boy! Warren I bet you never thought you would get so much info and be confused more than started? What are you intending to store? How close can it be stacked to the center or wall bearing partition?

Lets bring it back to the original post.

Craig or Mo, here are MA codes which basically mirror the International codes. Can we attach a sticky note for this link as so it is available to all. If the site uses it for a base code I can add NFPA 211 and the International Mechanical codes when issues conflict BTW both are 2003 editions NFPA and Mechanical. The same structual grafts and charts can be applied threw out USA
http://www.mass.gov/bbrs/newcode.htm

Warren it is possible to blow 6" over the OSB and not get involved in its removal and only increase the area you what for storage
or add R19 fiberglass bats layed as close as possible together