Need help working out a maths weight problem.

Probably very simple but i seem to be going blank with it.

I'm making a green roof on my shed. Shed is 8 x6ft, and i want a rough idea how much a soil bed 3 inches deep will weigh.

Rought idea as to an equation to use?

Thanks,

CX.

So if thats a total of 16 x 12ft of 3inch soil, could i just weigh a square foot of 3inch deep soil and multiply it?

Have a feeling this was easy and i was having a thick moment lol.

CX.

Assuming it is a flat roof 8x6 and 3 inches (1/4 foot) of soil that would be 12 cubic feet (8x6x.25). Since the density of soils can vary greatly then you would be best to weight it yourself. If you can measure a cubic foot of soil an multiply by 12 you should get your answer.

reply to post by fenceSitter


Lol thank you for that, confirmed my last post....must be old age, my minds not what it used to be....i was 40 last week after all.

Thanks.

CX.

Glad to help! Hope your green roof project works out well.

reply to post by fenceSitter


Yes to this. However, definitely weigh a kg first to give you a starting base. As correctly observed, soils are not universal. Sandy soil will weigh far less than clay rich soil, for example.

reply to post by Flavian


Cheers....i think i'll go for bagged soil, the compost type, i think thats lighter.

CX.

My suggestion would be to build a 1 sq. ft. box (same kinda construction as you're planning for the roof). Don't forget drainage and maybe sod if that's what you're putting on top. Then weigh it, then soak it and re-weigh it... it'll be a lot heavier with water. That'll give you a fair practical insight into what you're plans will need to accomodate. It could get pretty heavy I'd guess!

Just curious, what is the purpose of the this kind of roof on a shed?

Originally posted by surfin4it
My suggestion would be to build a 1 sq. ft. box (same kinda construction as you're planning for the roof). Don't forget drainage and maybe sod if that's what you're putting on top. Then weigh it, then soak it and re-weigh it... it'll be a lot heavier with water. That'll give you a fair practical insight into what you're plans will need to accomodate. It could get pretty heavy I'd guess!

Just curious, what is the purpose of the this kind of roof on a shed?

Thanks for that.

Well to be honest, mine is just to look nice on a shed rather than a plain roof, i thought about maybe a moss and heather one or the sedum roof carpets.

Here is a good video on green roofs that are springing up all over the world for all kinds of reasons. They have been used for thousands of years and can keep your house cool.

I just like the look of them.



CX.

you'll probably be looking at several tonnes of earth needed and most standard sheds cant take that so make sure you have enough support for a rugby team and their beer while playing with pogo sticks otherise it'll just collapse in on itlself

Heres a nice example, the kind of thing i'm trying for.....



CX.

I noticed an issue with your math. In your first post you said the shed was 8x6, and in your second post you said it would be 12x16. That is 4 times the square area where even if your roof was pitched you would need less than 2 times the area. You can use Pythagorean theorem to figure out the real area of each side of the roof. Trust me it will be much closer to the original 8x6 area (and no where near 12x16)

EDIT: If your roof was pitched at a ridiculous 60* angle (which is very steep, it is never done on roofs) THEN you would only double the area. The profile would be like an equilateral triangle if you can imagine that, and no roofs are build that way. I am guessing you can multiply the 8x6 area by 1.2 - 1.4 and get a safe estimate, but still do the math just to be sure.

Also when you sample a small bit of soil make sure you soak it to account for rainwater weight. Additionally you need to think about drainage. You dont want soggy soil touching wood or even shingles for any length of time. If you live in an area where it freezes, you need to think about 'soil creep'. All your soil will start piling up at the gutters and start falling off. You may need to respread the soil frequently (at least until a good thick root system is developed)

reply to post by CX


Here is a good place to find an answer...

www.abovetopsecret.com...

This guy really knows his stuff...and with assistance from technology...he can solve just about any mathematical question you can imagine!

Anyway...good luck with the flower beds!

reply to post by IntegratedInstigator


Thanks for that...yep, totaly got my measurements mixed up, it's the base of the shed thats 8 x 6, not the roof.

Thanks Jerry.

CX.

reply to post by CX


Well anyway...let's give this a go!

Using a simple area formula B * H * W = X...we come up with 8 * 6 * .25 (1/4 of a foot or 3 inches) = 12 ft.

So 12 sq. ft. per side multiplied by the weight of one square foot of soil (which is unknown at present)!

Your equation will look something like this 12 * X (X=weight of one square foot of soil) * 2 = How much the soil will weigh for your beds....also factor in the water weight at around roughly 8 lbs. per gallon when you are watering your flowers, herbs, etc...!

To be safe I would make sure your roof is capable of holding double what you are purposing!

Good luck and happy growing!

reply to post by jerryznv


Thank Jerry....off to measure dirt!

CX.

You could Google it and find that dirt weighs 120 lbs per cubic foot

wiki.answers.com...

this is good too

www.reade.com... rganics-ceraqmics

3" of dirt would be 120 lbs / 4 = 30 pounds per sq ft

A 10 ft x 10ft section would be 100 sq ft with 3" of dirt would weigh 3000 lbs.

if the roof will hold that load depends on the distance between the joists the span of the joists and the roofing material.

There are a lot of guidelines for calculating floor load on the web.

Originally posted by jerryznv
reply to post by CX

 

Well anyway...let's give this a go!

Using a simple area formula B * H * W = X...we come up with 8 * 6 * .25 (1/4 of a foot or 3 inches) = 12 ft.

So 12 sq. ft. per side multiplied by the weight of one square foot of soil (which is unknown at present)!

Your equation will look something like this 12 * X (X=weight of one square foot of soil) * 2 = How much the soil will weigh for your beds....also factor in the water weight at around roughly 8 lbs. per gallon when you are watering your flowers, herbs, etc...!

To be safe I would make sure your roof is capable of holding double what you are purposing!

Good luck and happy growing!

Again, it wouldnt be *2 unless the pitch of the roof was 60 degrees which is ridiculously steep. See my post above. if the base of the shed ix 8x6 then depending on which side the ridge line is parallel to, you would use pythagoreans theorum. I am going to assume the ridge line runs the long side (8 foot side, pretty common. Using pythagoreans theorum and assuming a few standard values, the length of the roof slope is 3.35 feet.

The area of one side of the roof is then 3.35*8 = 26.8 square feet. Multiply this by 2 to get both sides of the roof.

Total roof area is 26.8*2 = 53.6 square feet.

To find volume from the area take 53.6 square feet and multiply by 1/4 feet deep (AKA 3 inches deep (3"/12")

53.6 * 0.25 = 13.4 cubic feet of soil, based on loose assumptions I made on your roof.

If you would like an accurate number then PM me and don't listen to all the bad advice given in this thread.

For the purposes of this thread I assumed that the ridge was along the 8 foot length, the ridge was 1.5 feet above the 'gutters' giving you a 6 pitch roof, This means that the roof is fairly shallow. If these numbers are different then reply with the specific numbers (how high are the walls, and how high is the tip of the roof). Is the point of the roof on the 8 foot side or the 6 foot side? Better yet, go ahead and take a picture of the shed in question.

reply to post by IntegratedInstigator

If you would like an accurate number then PM me and don't listen to all the bad advice given in this thread.

Really...now thats not very nice!

Should your advice be included...or just everyone else's?

I don't know about bad advice...seems you are spilling it out pretty thick with comments like that!

Again, it wouldnt be *2 unless the pitch of the roof was 60 degrees which is ridiculously steep.

Huh?

There are two sides to this roof and neither side cares about the pitch...we are talking about weight and volume!

There is a formula for figuring in the pitch and load capacity...but really that wasn't the question...and yes..it is multiplied by two...jeez!

Originally posted by jerryznv
reply to post by IntegratedInstigator

 

If you would like an accurate number then PM me and don't listen to all the bad advice given in this thread.

Really...now thats not very nice!

Should your advice be included...or just everyone else's?

I don't know about bad advice...seems you are spilling it out pretty thick with comments like that!

Again, it wouldnt be *2 unless the pitch of the roof was 60 degrees which is ridiculously steep.

Huh?

There are two sides to this roof and neither side cares about the pitch...we are talking about weight and volume!

There is a formula for figuring in the pitch and load capacity...but really that wasn't the question...and yes..it is multiplied by two...jeez!

edit on 2-6-2012 by jerryznv because: (no reason given)

No, it is most definately not multiplied by two. If the base of your shed is 8x6, then how do you have two sides of a roof each measuring 8x6? Also the pitch does matter so that you can get an accurate area for each side of the roof, only so that you can calculate volume using a 3" soil depth.

I didn't mean to cut that deep with the 'bad advice' comment, and I apologize for offending you. Seeing the thread you authored on starting a Mathematics Forum, I gather you are comfortable and well versed in various maths. Knowing this I am confident you will see where you went wrong after seeing the graphic I threw together in my following post, showing how to properly calculate the area of a roof.

ETA: See my post on the next page, where I included a graphic to explain what I am talking about.