Replies

1. 
   frenchy | Feb 15, 2008 01:09am | #1

   Tommymc

    I'd stay off the roof completely.. why add your weight to a roof already loaded with snow? (aside from it being slippery and you could fall)

     Let's assume that somehow your building inspector didn't know what was needed with regard material strength and some of the boards are about to fail..

       1 adding your weight won't improve the situation (I know I said that already)

       2 It's slippery (ditto)

       3 You have insurance.

       4 chances are it's OK as it is. 

                I once loaded a spot on a floor up with a second story,

                 a Grand piano upright,

                 2000 bd.ft. of green lumber   that was on a (one)  2x8 24 inches on center. 

                  It cracked.. 

                  and was still cracked years later when I tore down the house..

                   (never moved the load)

     

2. 
   MSA1 | Feb 15, 2008 01:10am | #2

   Code book specifies Snow load dependant upon your region. If you're really worried, throw a heater in your garage for a few hours. The rising heat should help you avoid the shovel.

3. 
   Riversong | Feb 15, 2008 01:40am | #3

   Assuming your framing is SPF#2 or equivalent, your roof is rated for only 14 psf snow load (assuming 10psf dead load).

   Compact snow weighs approximately 1 psf per inch of depth.  So your roof is rated for a little more than a foot of dry, compacted snow. 

    

   Riversong HouseWright

   Design *  * Build *  * Renovate *  * Consult
   Solar & Super-Insulated Healthy Homes

   
   

   ---

   Edited 2/14/2008 6:03 pm ET by Riversong

1. 
   frenchy | Feb 15, 2008 02:53am | #5

   Riversong, 

       you should mention the built in safety factor in those calculations.. I'd hate for that person to worry if he has 12 1/2 inches or some other slight overload that in all probability the roof will shrug off easily..

    You could also mention tossing some rock salt on  the roof if it's really deep.  a 50 pound bag of water softner salt will melt a lot of snow overnight..

    Hey while you have your load chart handy how much overloaded was that 2x8 joint?  it was SPF spanned 10 feet and was 24 inches on center. Thus the full weight of the piano,  the whole second story above and about 1/2 the weight of the wood say about 8000 pounds. 

    Just courious how far overloaded a joist can get before it shows signs of failure..

   Edited 2/14/2008 6:57 pm ET by frenchy

1. 
   Riversong | Feb 15, 2008 03:55am | #6

   I'd have to see a schematic of that loading before I could even begin to offer an answer.  And loading on a single member depends on the quality of that member.  Plus it's difficult to determine how much load sharing the subfloor/flooring would offer. 

   Riversong HouseWright

   Design *  * Build *  * Renovate *  * ConsultSolar & Super-Insulated Healthy Homes

2. 
   Danno | Feb 15, 2008 04:17am | #7

   I'd be careful about throwing just rock salt up there--it can play havoc with all sorts of things (like flashing or an other metal it contacts and where the melted salty runoff lands--may kill shrubs, etc.). But there are ice emlting salts made especially for roofs that may work. There are also "rakes" with long aluminum handles that can be used from the groun--only problem with them is you are pulling the snow down on yourself!

1. 
   frenchy | Feb 15, 2008 06:00am | #10

   Danno,

    I wouldn't recommend it as a normal course of things (rock salt on the roof)   but in the event of severe snow storm that much snow will wash the corrosive effects of salt off the roof quickly.  Minimising any possible real damage..  

     Back when I had the old house with it's relatively flat roof and major overhangs  the  ice dams that formed I used to put nylons filled with rock salt  up on the roof to melt a trough thruough the ice dam about every 4 feet.. The first ice dams occured usually in December and I'd toss the nylons up there about every 6-8 feet..  by march the nylons would be empty of salt and I wouldn't have the effects of any backed up water..    That went on for better than a decade and when I tore off the roof nothing was damaged.. not the aluminum gutters,, roofing nails or anything..

1. 
   Tommymc | Feb 15, 2008 06:47am | #11

   Well, there are no signs of sag or strain on the roof yet.  It's just that it's turning out to be one of the snowiest years on record and my garage wasn't exactly overbuilt.  I'm estimating close to a foot on the north side but only 6-8 inches on the south.  So barring any heavy rain, it sounds like I'm still in a safe zone.  I might look into a roof rake just to be safe though.  No Lamborghini but I do have a '60 Chevy parked in there that I'd hate to have damaged.

   Edit:

   I took a better look in the daylight this morning.  There's a lot more snow than I said above. More like 12" on the south side and 18"-20" on the north. Light to medium density snow. I guess this will have to be the "Year of the Rake"

   Edited 2/15/2008 6:22 am ET by Tommymc

4. 
   reinvent | Feb 15, 2008 01:45am | #4

   Get one of these and save your neck.

   http://www.amazon.com/Avalanche-Original-Roof-Remover-System/dp/B00004WZ5D

   http://www.mengo-ind.com/displaysection.aspx?which=80

   http://www.snowcutter.com/

5. 
   Danno | Feb 15, 2008 04:25am | #8

   You probably read my reply to Frenchy about salt, but just in case you didn't, you may want to use salt made especially for use on roofs. There are also long handled aluminum "rakes" you can use from the ground to pull the snow down with.

   The failures I've heard about are where you have a tolerable load of snow and then it rains and saturates it, or a heavy, wet snow falls on top of it, or you get freezing rain. That can tend to make it too heavy and the structure fails. Do you see any evidence of overloading--rafters sagging or anything?

   I guess I wouldn't park my Lambourghini (sp?--you can tell this would not be a problem for me, since I don't even have one and don't even know how to spell the name!) in that garage until the snow melts though!

6. 
   Jeff_Clarke | Feb 15, 2008 05:42am | #9

   Here's the most effective way to do it - http://www.youtube.com/watch?v=gPcBxcYkiMg&feature=related

   Jeff