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The M3500 Foundation Deck Bracket is constructed of 3/8" 50W structural steel which is the same steel used to build structural bridge members. Our engineered design uses center point load technology. The side flanges ensure a correct installation of the deck support post to ensure the proper weight distribution over the center supporting flange. Each bracket is comfortably load rated for 3500 lbs and the recommended spacing is 8' intervals. Our supplied custom grade 8.8 sleeve anchors are rated for 3000 kg or 6600 lbs each.

With the introduction of heavy composite decking materials more load is being placed upon the ledger board of decks. Typical current installations is to bolt or screw the ledger board to the side of the house. Quite often the bolts or screws miss their intended connection or are put through a veneer of brick or siding. Over time these connections deteriorate allowing the deck to fall off with the severe potential of personal injury.

The M3500 will eliminate these potential problems by transferring the entire ledger weight load to the house foundation. The M3500 is a solution to an the age old problem of falling decks. Deck safety is a priority.

Building departments across Canada and the USA are beginning to mandate that all ledger board weight now be transferred directly to the foundation of the house. All decks will now be required to have additional support via a 6x6 PT post into a foundation attachment. The Mammoth M3500 is the solution to this issue, an easy 15 minute install and it will save time and money.

Why Do Decks Fail?

The most common reason for total deck collapse involves the deck “pulling away” from the house. This type of failure typically occurs because the ledger board was not properly attached to the house. The vertical shear weight causes bolts to release from their anchors which create the pulling away action.


There are many construction aspects that go into ensuring the ledger board is properly attached. Primary Questions: 1: Were lag or carriage bolts used? If so, are they the correct type, size, spacing, stagger, and depth? 2. What was the ledger board connected to? 3. Was flashing used to prevent water damage?


Nationally, deck builders/DIYer’s are attaching decks to homes by simply bolting them into the veneer of the house thinking it will hold the weight. This is incorrect.


Even the building code is not 100% safe. Building code states to use a carriage bolt with washer and go through the ledger board, then use a spacer and go through the veneer (brick or siding) and through the sheathing and then finally through the rim joist of the house and finish it off with another washer and bolt on the inside of the house (see diagram below). After this, you still would not get the proper strength for any deck. The building code method only gives 1 1/2” of actual load support (the 2”x 8” rim joist) as the veneer and sheathing is not load bearing and the 1 1/2” on a 10” bolt is just not sufficient enough to carry a deck safely.


Also keep in mind, with the introduction of composite deck materials, the method of attaching a deck to a house has not changed, but the weight of composite decking materials has tripled, maybe even quadrupled depending on the structure. The ways in which a deck is used today has changed dramatically over the years with more people using decks as outdoor living rooms. The live load on decks has increased from 40 psi to almost 150 psi. The average live load capacity of the ledger board on a 20’ wide deck has gone from 4800 lbs to almost 18,000 lbs in many cases, but the attachment of the ledger board has not changed. This is a problem!


The current approved method of bolting the ledger board to a houses rim joist should only be used for lateral support. All load weight should be transferred to the foundation of the house for maximum load capacity.  


Follow these steps to insure proper installation of the M3500.

Each M3500 is provide with four 6" sleeve anchors

There are 2 methods to use the M3500 properly

Method #1: Bolting through the Veneer and rim joist of the house and into the foundation.

Using a double 10” ledger, use a carriage bolt and go through the veneer and rim joist of the house.  Use a washer and nut on the inside of the house to fasten the ledger board. Use the provided 6" sleeve anchors to bolt the M3500 to the foundation. Once everything is bolted properly and attached to one another, the bolts that are holding the ledger board in place will act as the lateral support . The M3500 will act at the shear weight supporter. 

Method #2: Bolting to the foundation only.

Use the provided 6” sleeve anchors to attached the M3500 to the foundation of the house. Install front and side lateral supports on the front beam/post assembly. (Please make sure you follow the correct building code requirements when installing your lateral supports.

***Additional Notes: When using the M3500, you must following all proper building code methods when building a deck. The M3500 is just to support the LEDGER BOARDS for the deck.*** 

Where strength Matters!!

Tested and proven.

The M3500 was tested and certified by Intertek Canada, a third party company that tests products on their performance. The testing was carried out on 4 M3500 brackets and the results were outstanding!!! With an maximum payload of 96,440 lbs, with a 4/1 safety ratio, giving the M3500 a safety load factor of approx. 24,100 lbs per bracket. 

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You can purchase the M3500 Foundation Deck Bracket here or through one of our resellers below.

Problem, and our Solution!! 

For more information or to place an order for the M3500, please fill out the form below. 

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