Building a room under an open deck so it is water tight?

Hello

I have seen many rooms under open decks fail do to water leaks and be torn down after a while. It was not in the budget to build a second story room so a little shack under the deck for a workshop seamed to be a good solution and to store wood pellets.

Has anyone seen or done this successfully?

In this day and age with all the modern building materials, it does seem possible?

So in this bold attempt, I went with a full foundation 48" deep and polished concrete floor.
The foundation is 3,000 lb mix concrete and the floor is steel reinforced 4,000 lb stone mix with synthetic fibers to prevent micro cracking during the curing process poured over a base of 3/4" stone with sandy soil as the sub base. The 3/4" stone base allows for good drainage to prevent frost heaves.

Since the roof span is 12' and 1" of width is required per foot af length we used 2x12s. Then shaved them on an angle for a little pitch to shed water.

Next we chose Advantech premium wafer board which is far better than the old OSB junk that first came on the market.
The ability to NOT absorb water, hold the fasterners and stay stiff is very remarkable!
See video
http://www.huberwood.com/advantech/video/sIpwFgcZdzU

Two crisscrossing layers of Grace Ice and Water shield were layed on top of the sloping advantech and 6 inches up the side of the house under the shingles.

Now the shaved runners are being screwed back to the top of the shaved 2x12s with still some pitch to secure the open deck boards.

The Deck will be built using Fiberon composite decking and Fiberon railings.

See pics below.

 

Interesting! There have been many disasters doing this type of project even my contractor's dad built a room on their house under the deck that had issues and had to be torn down, so this time we are more determined to do it right and there is enough pitch to wash away debris. Even so, the Advantech roof used for sub flooring does not rot! I only know of one other success story and we are doing it the same way.
We did a concrete floor so there is no chance of mold problems too!
Thanks for your comments Jay!

 

Don, a concrete floor doesn't prevent the possibility of mold problems.

 

True if the floor is below grade, however if it is level with grade them concrete does help a lot. If a wood floor is used then the code here is the floor must be enough above grade to have air flow under it to prevent mold. In this case it would reduce headroom since the deck above it cannot be higher than the door into the house.

 

How are you preventing the roof portion of the room from separating from your existing structure. I looked at putting some storage under my nice long deck on the back (front) of this place and came to the conclusion that it wouldn't work too well except as just covered and not walled at all? Houses move so joints can part and even a small parting can let in tons of the wet stuff.

 

Good question Smokey. Since the walls have a good foundation that meet the house structure, the roof joists are hung on a ledger board bolted to the house structure. The double layer of grace ice and water shield on the roof also go up 6 inches on the house under the shingles that were removed and will be put back on. If I had known about 60 or 90 mil EPDM rubber roofing I may have went with that. However it is more expensive than 2 layers of Grace.
If you uses a ledger board like all decks use, would that work for you?

 

Don I understand the grace I&S and EPDM (got quite familiar with that stuff dealing with a flat roof), but ledger boards work well provided both the house they are attached to and the new wall move in concert and you have the proper fastening system. Improper fastening via ledger boards is a leading cause of deck failures. I had to do some remedial work on this place to correct just that possible issue.

 

Oh, yes I understand. The ledger board is bolted to the studs in the wall of the structure and the foundation goes down 48" and was pinned to the existing foundation with ReBar. I have a Master carpenter doing this new deck and I am avoiding all the errors of the prior deck that was very shaky and done by a contractor that could not write in English!

 

Not so sure I can write English either but I understand frost effects and movement induced problems. Also I hates digging for footers. The I&S should go up at least 6" above the snow load on the area's height. It can get high on that deck and against the house where believe it or not water will be against the siding.

 

Not sure if this will help but it keeps the mud room entrance dry as popcorn.

Water filters through deck.
Corrugated metal slopes down to gutter then out.
I have no need for walls but you certainly could incorporate them.

 

yeah I did a covered deck over deck with polycarbonate skylights so Deacon would work. I have PT deck boards quarter inch gap 2.5 inch drop in 12 feet. it's dry. I you want to insulate and heat. it can be done with rubber roofing but make sure of all seams!

 

Hi smokey
Yes, I have a Master carpenter doing this job and after talking to him today, he told me the contact type glue used for the EDPM rubber roofing is not nearly as good as the sealant used in the Grace Ice and water shield so we went with 2 layers of Grace.

 

Hi Don, my wife loves you hoarder guys and asked my opinion. Grace is not an exposed roofing product, it is an underlayment. EPDM with bonding adhesive included is 2/3rds less the cost of two layers of Grace. Adhesives are not the issue, Grace was never designed as an exposed surface membrane product even in any amount of layers. The worst issue now is that the roofing system does have many overlapping seams in two layers that will eventually fail and a deck tear off to investigate leaks. The substrate is not an approved roof decking, it is stamped flooring. Sorry, WildWest you married an honest roofing company owner not a Master Contractor.

 

I guess the word water tight in the title post set me off as WildWest is not contractor and likes to think of hoarders as family

 

look into techna-pole. 2 inch stainless steel pipe with disc on bottom. coated in a heavy plastic that slides and up and down post. frost acts on plastic sleeve guaranteed for life about same cost as digging footing, ConCrete big foot etc.

 

I really didn't want to get into this except to let Don know the primary reasons that things attached to a house after it was built fail. Master whatever holds no weight in my book and it shouldn't in Don's case seeing he is an engineer. Most people also have installed items used as flashing incorrectly for decades. Keeping water out requires a lot of work, the things I get a chuckle out of is skylights, nothing but leaks waiting to happen. I have a deck that runs 48' along the front (back) of this place if I don't shovel the deck at least a path next to the siding and the snow/ice/water accumulate it can easily go 3' or more up against the siding now do you think most builders would flash that high?

 

I agree that Grace states it is underlayment. As a roofing contractor you have guidelines and must use the products as they were designed. Sometimes using them in a different way can prove fruitful. Like using Nitromethane for car gas. As a former dragster, it sure makes the car fly! SUNDAY !!!

 

Smokey, I agree with you 100% here. This is a really tough project to make waterproof and there have been many failures over decades. Since I am an engineer and I go with the best products and not necessarily the way contractors or carpenters have done it in the past. The main structure has been there for 53 years and probably will not settle anymore, the codes are now 48" for a foundation to prevent settling and yet does not work for swampy and other areas. I know my area and the 48" foundation pinned to the main structures foundation is the best anyone can do. As for the roof and materials, the Advantech flooring has been proven in test to be better than plywood or anything else on today's market period. If the EPDM is so good then why must it be installed in one piece? I have seen how the Grace I&W works it is on my shed. Yes it is an underlayment but with a deck on top it will not be exposed very much at all. I could put aluminum on top but that is overkill in my opinion. This is where we must do the best we can and yes there are nay sayers and there always will be.
So we will see and I can keep updating and reporting on this method that I choose. We numbered all the 2x12 cuts and bolted them back on today, so now we can build the open dock with Fiberon Decking.
Saturday it Poured heavy and with one Layer of Grace there were NO leaks. Yes 2 layers of grace is more money but by crisscrossing the seams it just maybe the absolute best way to go!
Nothing good is cheap and easy!

Although EDPM is popular with roofing contractors it does have it's problems
For More info See http://www.coolflatroof.com/rubber-roofing.php

 

Code considerations sometime prevent certain items from being used. YMMV.