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15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
15 MOST COMMON DECK CONSTRUCTION MISTAKES
Feb, 2012 Mistakes to avoid
The 15 most common mistakes are easy to avoid, we look at the
main causes for these mistakes and how to avoid them.
Matt Shutkowski
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
FOOTINGS
#1- Hitting underground water, power and/or gas mains
The consequences of hitting a water, power and/or gas main have the potential for serious to fatally
injuring you! Not to mention the inconvenience of not having no power or water. So to avoid this
unnecessary and dangerous frustration, do all your checks with your local government agency and
service providers (call “Dial before you dig” on 1100 in Australia). Once you have the locations for the
services, mark them out on the ground when you mark out your footing locations so as not to hit them
when you dig your footings.
When you dig you footings it is highly recommended that you dig them by hand with a shovel and
crow bar. This way if you are unfortunate enough to hit one, you have more chance of not seriously
damaging the service.
Something to keep in mind, if you hit a water, power and/or gas main and you have spoken to “Dial
before you dig” and have done as much as possible for locating the mains, you will greatly minimise
your liability.
#2 – Timber posts rotting away within a few years of the deck being
completed
There can be many reasons for this, the most common are as follows:
i- Timber posts that are concreted directly into the concrete footing.
This is a problem because concrete is porous and absorbs ground moisture. This has the
timber post be continually moist, the perfect environment for timber rot. The post will rot in
the location shown below the quickest, as it is the last place to dry out and the first place
to get wet.
Concrete
footing Timber
post
Where the rot
most occurs
in timber
posts
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
ii- Timber posts having gardens or dirt/soil built up around them and/or touching the timber
post will cause the post to rot. Below is a picture of a timber post that has rotted away
because of soil build up.
To solve this problem the best way is to install galvanised stirrups into domed concrete footings where
the base of the timber post is raised 75mm above the top of the domed concrete. This also allows for
any water to run off the top of the concrete footing which greatly aids in the life of the galvanised
stirrup (a stirrup is a metal bracket that holds the timber post out of the concrete).
75mm gap between the
domed concrete and
timber post
Domed concrete
Hot dipped galvanised
steel stirrup
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
#3 - Sinking deck frames
The most common reason is incorrect footing size, normally due to not having an engineer design the
structural components of the deck. Any other reason is the owner bolts the deck posts directly to an
existing concrete slab that is untested, usually a pathway. Most concrete paths over 20years old do
not have any form of concrete/steel reinforcing.
The best and only recommended way to install deck posts is directly into dug footings using galvanised
steel stirrups making sure the footing hole is dug straight down and not what is called in the industry
“belled”.
SUBFLOOR FRAMING
#4 – Deck floor sagging
99% of the time this is due to incorrect timber/timber size being used. If you have an engineer design
your deck you will not have this problem. The two main types of timber is softwood (all types of pines,
etc) and hardwood, as you can imagine just by the name one is stronger than the other. You can swap
softwood with a hardwood and not have a problem keeping in mind that you must use structurally
rated timber. However if you go the other way, swaping hardwood for a softwood (usually done in
an attempt to save money) you will have major problems if not a collapsed deck.
The sides of
the hole are
curved and
rounded
Belled hole
The sides of the
hole are straight
and flat giving a
square shape
Square hole
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
#5 – Timber cracking and breaking
Aside from swapping hardwoods for softwoods as mentioned in the above problem, this is most
commonly caused by too much timber cut out of the joins. The maximum amount of timber that can be
cut out of a joint is 1/3 of the height, width or thickness. There are a few ways this can be measured:
When more than 1/3 of the timber height, width or thickness needs to be cut out additional support
needs to be added. This can be in the form of metal brackets.
A hole can only be a
maximum of 1/3 the
height of the joist.
Joist
1/3 max
Bearer
Joist Here you can see in red
less than 1/3 of the timber
in the joists height has been
left to sit on top of the
bearer.
This is where the timber will
crack and break due to the
little amount of timber
sitting on top of the bearer.
More than 1/3 – Not OK
Less than 1/3 - OK
Bearer
Joist Here you can see in
red over 2/3 of the
timber in the joists
height has been left to
sit on top of the bearer.
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
#6 – Bolts, nails and steel rusting
USE GALVANISED BOLTS, NAILS AND STEEL!!!!!!
This is not optional. You will have your deck start to fall apart in a matter of months if you do not use
galvanised bolts, nails and steel. Galvanising is where zinc coats the steel, usually done by dipping the
steel into a molten vat of zinc. Zinc as a metal is more corrosive than steel, so when steel is coated in
zinc the zinc will corrode before the steel corrodes. This in turn will leave your steel corrosion free for
a very long time.
DECKING
#7 – Black and other marks on decking boards
The black marks are caused by leaving metal on a wet deck. The only way to stop this from
happening, is to clean the deck after each day of construction. Pick up all tools, nails, bolts and
anything else metal and sweep the deck down. When you nail in nails there is a small amount of metal
filings that fall off the nail when hammering it in. Finially do not use a grinder on the deck or
anywhere near the deck or where people will walk on to the deck. Grinding sparks leave metal filings
everywhere and as you will see in the pictures below leave a very ugly mark.
Galvanised bolt
versus a non-
galvanised bolt
A non-galvanised
steel beam. Make
note of the amount
of rust that has
occurred.
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
There is a couple of ways to remove these black marks however it will take a lot of elbow grease:
Option one- Clean the deck with a product called “Deck clean” (a mild acid) and scrub like you have
never scrubbed before;
Option two- Sand the marks out, best to do this by hand as power sanders can end up making more of
a mess than the black mark itself.
Grinding
sparks
Bolt &
nail marks
Bracket
mark
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
#8 – Decking boards not installed to a straight line
There are many ways to install your decking boards in a straight line. The easiest way to do this is to
use a chalk line (a chalk line is a string line coated in chalk that when you flick it leaves a straight line
of chalk) and mark out every forth/fifth board (called a grid board) and completely nail that board
to every floor joist. Once you have installed all the grid boards, place all the other boards in between
them and use wedges to evenly space the boards between the grid boards. Make sure when you do
this that you allow a 2-3mm gap between each board.
#9 – Greying and rotten of decking boards
This can be caused by not coating the deck with a decking oil or stain once the deck was complete. This
is also caused from not maintaining the decking oil or stain in years to come. If your deck is does not
have a roof over it, the sun will deteriorate the coating faster than a covered deck. A good rule of
thumb, is that the moment any of the coating is starting to fade or look grey it is time to re-coat the
deck.
Grid
board
Grid
board
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
ROOF FRAME, ROOFING & CEILINGS
#10 – Losing your deck roof in a severe storm
To avoid this you need to engage an engineer to design all structural aspects of your deck. This is not
a recommendation, this is a must. If you build your deck without the appropriate engineering and
something goes wrong, you are liable. If someone gets hurt you can be charged with assault etc.
#11 – Leaking roofs
The most common and sometimes not the most obvious reason is that the roof screws have been over
tightened. The roof screw has a rubber washer at the base of the head of the screw. This washer
seals the hole that the roof screw has made in the roof sheet when screwed. When the screw has been
over tightened it squashes the rubber washer and breaks it, allowing water to enter into the screw
hole. See below.
#12 – Sagging ceiling
The most common reason is the ceiling supports are positioned to far apart. Once the ceiling is
installed, the ceiling maybe flat and straight. However over time usually in about 6 months moisture in
the air will soften the ceil enough for gravity to start to sag the ceiling sheets causing a wave like
effect on the ceiling.
Rubber washer
Screw tighten correctly where you
can see the intact rubber washer
Screw over tighten where you can
see the rubber washer has broken
away from the screw
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
STAIRS & HANDRAILS
#13 – Out of level stairs
When the stair set height is measured, called the “rise” (height from ground to top of decking boards)
this has been measured straight down from the edge of the deck however not where the stairs meet the
ground, called the “run” (distance from edge of decking board to front edge of bottom step tread). In
the diagram below you can see the height difference between straight down from the edge of the
deck compared to where the stairs actually meet the ground. If rise height is measured close to the
deck and not where the stairs meet the ground in you will have too many/not enough step treads
required for your set of stairs. This will result in your step treads either tilt forward or backwards.
Deck
Post
Ground
Rise
Run
15 Most common deck construction mistakes
Matt Shutkowski © Copyright 2012
#14 – Stairs handrails to low
Firstly if you don’t know what the minimum height of handrails are, check with your local building
authority or engineer. The top of the handrail is measured straight up and down from the top front
edge of the step tread which is called the “nosing line”. The nosing line is an imaginary line that runs
along the top front edge of every step tread. This is where your local government agency will
measure your handrail from, to check that the handrail meets building regulations.
THE BIGGEST MISTAKE MADE
#15 – local government agency having the deck changed or removed
This is a very easy mistake to avoid, get your deck approved before building it. If you choose to try
and do it without the correct approvals this can end up costing far more than just local government
agencies fees saved. The local government agency may not have you remove the deck, they may just
want you to change the size or even location of the deck. As you can imagine this is going to be a
major re-work for your deck.
Deck
Nosing Line, always measure
to the top of your handrail to
this line.
Handrail
Where you measure
your handrail from