Hydraulift Lifting, Lowering and Restumping services

Tuesday, 29 December 2015

The early signs

Windows getting jammed, doors getting hard to close or a feeling of drunkenness when chartering the house, a few of the symptoms of deteriorating stumps or house posts.

There are many more signs such as the roof leaking, excessive creaking at night(this is damaging your building) or through weather changes etc however the first mentioned are the early warning signs.

It can be a serious expense re-stumping your house however not near as expensive as it will get if left unattended. Those sticking doors and windows are under a lot of strain and are receiving damage as the situation gets worse. It's hard to notice the deterioration as it happens over a long period of time. 

There's two things happening constantly with timber posts. The first is their sinking usually not all but the ones holding structural weight are the first to start. Secondly their rotting, as the outside more sappy part of the timber falls away with rot there becomes a gap, sometimes very noticeable sometimes not so obvious but it's there. This lessons  the resistance around the post and narrowing it like a spear at the same time which over time gets worse and worse.

When the post subjected to the structural weight and pressures sink it puts pressure up through the roof and down to the posts in that area which puts excessive weight in the area leading to further problems.

Due to the amount of posts under a house it can take considerable time before the situation gets extremely damaging and to the point of unsafe however there will be no warning bar the creaking and aforementioned symptoms. At some point it will become unsafe in high wind areas and flood prone areas but there will be no warning at that point.

Safety or expensive damage? Mostly expensive damage, fixing doors windows and leaking roofs are expensive operations, getting to the timber joints that have been worked loose over years of the house crab walking downwards can be somewhat of a challenge. In addition to all this weather gets in and rots timber that needs to be replaced and so on and so forth.

If you act on the early signs often you may simply need to replace a few posts at a time and possibly over an extended period of time as keeping the floor level will slow down the deterioration to no end.

Understanding an unlevelled building

Simple you would think, the floor sags push it up again and we are good to go? No stop! You will most likely bring about some more complications. In most cases the building sag has been there for so long that it is very difficult to work out exactly where the problem is. 

Looking at the hand sketch following you can see, that as a centre post near a structural wall sinks then additional pressure is transferred to the outside posts. It does this because the roof ties the building in like a sealed box.

These outside posts are subjected to the weather and usually deteriorate more rapidly, however it is inside the house that receives the traffic. Normally a well used hall etc abuts the area of internal structured walls and with heavy traffic it's these posts that will sag first transferring weight to the deteriorated outside posts pushing them into the ground like a sharpened stick or spear.

It can be a case of the chicken and the egg, a post near a staircase on the outside might receive heavy traffic transferring weight elsewhere however it is normally the case first mentioned.

Also a lone stump or group of stumps on the outside that don't sink with the building can put enormous pressure on the centre structural wall and over time timber joints get weaker and timber sags it will look! like is is sinking severally in the centre whereas it's being pushed down hard at that point.

Not withstanding this it needs to be evaluated, it can be done with a trained eye looking at tell tale signs as to what has happened but the simplest is a lazer level and create a model space showing post heights.

This needs to be done irrespective of whether you are completely restumping or peace meal with a few posts at a time. Not necessary if your changing the height of the building as a steel frame can be installed to take all the weight in the order of achieving a lift or a lowering of the building.

If you try to lift it and your wrong you will find extreme pressure on your jacking apparatus. That is if you jack on the outside because you noticed it had dropped in height there but it was the inside that saged first then you will be trying to lift the house taking most of the weight on one point and will most likely result in breaking bearers or stressing timber joints. In this case you would need to work out from the centre to the outside utilising the little bit of give the building has stretched, jointing etc and this will also transfer weight back to the centre as you go.

Levelling a building

Once you have collected your heights from a laser its time to work out where is or where is going to be level. Taking into consideration buildings that are permanently attached and other fixtures the level point may be able to be varied or it may have to be at a particular height.

The lowest point of the building may not be the lowest pressure point! A lone high stump on the outside of the building can push massive pressure down so starting from the lowest point of the building the bearer can be jacked up slightly to see how much pressure is on it at that point. If there is very little and it seams to go up effortlessly then keep going it will most likely go up to level relatively easy, however stop if it seams to get heavy leading into a counterbalancing system of support for the structure.

If all goes well at that point and your able to lift the building to approx 50mm above your predetermined level point you can proceed to support the building useing counterbalance technique described following otherwise you will need to find the post that are pushing the weight down, usually the highest one(s) on the outside of the house. Then working around the perimeter starting from this post or group of post work both ways around the building bringing the outside up to the same height as the starting point or high post(s) that is causing the pressure on the centre.

Once you've done that you should be able to return to the centre and start counterbalancing the structure.

Starting from the lowest point now defiantly close to the centre of the building lifting can commence. A post is going where the old one came out of so a suitable support needs to be put centre of the two holes and it needs to start on a reasonably continuous bearer so consideration can be given to a post under a bearer close to the lowest point or centre of the house as the case may be.

At least 4 steel frames will need to be incorporated into your levelling process however most of the rest can be props made from the post themselves or some other suitable means. By incorporating at least 4 frames your holding it from moving forward backward or sideways and depending on how long it will be like this will determine the extent or quality of your centre supports.

As you move from the centre out you can counterbalance long sections of bearer leaving the under part of the house relatively clear and keeping in mind that we are lifting to 50mm above level, not! level reason to which will become obvious when it comes time to hang the new posts from the bearers, ultimately allowing for precision accuracy. 

Heavy sections can be ascertained by looking for condensed internal structures such as rooms, wardrobes etc and place your support nearest to centre of these hot spots. It is sometimes very obvious which part to jack from that will cause it to spring up and counterbalance other times you will need to look inside and out and trial different locations. As can be seen the counterbalancing allows you to keep clear with minimal support hindering the rest of the processes.

Removing the old posts

If you have a crew there's no need to wait theirs an narly task ahead digging holes in a confined space. A few common sense issues are probably best observed here like don't put your hand on the end of the sawn off shovel you custom made to work in the holes otherwise when your tired and your hand gets crushed between it and the bearer considerable time can be lost.

The outside posts are the easiest to remove, a 4wd and or a winch will do just nicely dig a hole or shute to the side of it so it has somewhere to go and loosen up a little around the posts to reduce side friction and more so the suction cup effect. 

The inside ones get more difficult where the narrow clearance becomes more of an issue. A chainsaw and cut the top half of the post off is a good way to start especially if you are useing them to prop as you go.

Back to the holes, big dark and deep, sizes of the holes will vary accordingly to your soil assessment and council submission and approvals but as a guide for an average low set house 900mm deep by 500mm in diameter would be fairly standard. 

A small jackhammer can be worth its weight in gold here hardened clay and rock are common place in most areas and picking away at it with a custom made crow bar can prove long and tiresome.(for a simple custom job on the bar cut a norm in half gives you one for your mate)

Hanging by a thread

It becomes clear at this point you needed the gap so you could hang around. Not so clear? It will be.

When we levelled the building we needed to take it up 25mm to 50mm higher than the level plane or post height stump plan that we decided on. Now we can hang each post from the bolts bolting it to the bearer, adjust the height of the top of the post by winding the thread up or down as shown in the following illustration.
(A) bolts with long thread
(B) bearer we are bolting to
(C) post top

We are getting ahead of our selves, first we need to make or purchase the posts. They come in many different variations to suite many different scenarios for reasons such as wind strengths or seismic activity. 

Your building plans will specify sizes,how many and where there going etc as you would have gone through this with the engineer who drafted and engineered your new stump plan. However they won't show how and what tags you will need as they rarely would provide such detail. 

The bearer in the illustration above shows one continuous bearer left to right however they are often a junction of two bearers so it will have 3 tags in a T shape, the corners of the building will have two bearers intersecting at 90 degrees so the top of the corner post will have two tags at right angles, some variations are shown in the illustration below. 

Bottom line is every post needs to be planned by inspecting where each post will sit, how it will be bolted and what top support it needs to provide until you have a plan. You will be able to work out how many T's you need, how many straight through,s and how many right angle post tops you will need. As you may find out it doesn't always end there sometimes 4 tags are required and sometimes the tags or bearers run off at angles. There's only one sure way and that is to walk around and work each one out. 

The length of the posts will vary with sloping ground each post height will also needed to be recorded or drafted on your post making plan. The length of post in the ground doesn't change so you can measure the distance from ground level to the bearer at each location.

Image showing corner post and concrete finishing lower to allow for a concrete pad at a later date.

Once you made the plans for the individual posts, you can make the posts and it's time to hang them.

Holding them up one at a time in the location they are going is among the easier ways however two things need to be observed first, is the bearer straight and where each post will attach so that they are even and therefore a straight line at the top is achieved. 

A string line is always good but the top of the posts need to be in a straight line if you string line the bottom. Highset houses dual string lines top and bottom are advisable as you want them plumb and straight and high posts are very noticeable if they are out and can prove difficult to build onto if you decide to close in the bottom storey or build additions. 

If you have very straight bearers and lowset at around 900mm a level all round will most likely suffice.

If you skimped on the clearance height or the height above the level plane you may run into difficulty's here. If the top plate of the post comes in contact with the bearer before or at level point it will push the post in one direction or the other proving extremely difficult to hold plumb while you pour concrete. The posts need good clearance however to much will also hinder you ideal is as stated previously 25-50mm.

At this point your ready to pour concrete plumbing each post as you go. There are a couple of things that should be done at this point for rust prevention. A painted on membrane that is applied to the post 100mm either side of where the top of the concrete finishes and heap the concrete up to a mound highest at the point closest to the post so that any moisture runs away from the post and not into it or sitting around it. 

The only time this can change if the holes or posts abut a concrete pad, then you need to finish at a point that won't hinder the concrete pad at a later date, usually finishing just below ground level will suffice and it is highly recommended you put a concrete bonding solution on the top of the post hole concrete to stop moisture penetrating and sitting under the slab. 

This is shown if the image above where the concrete finishes low compared to the image following that shows it heaped or mounded up to the post.

Image showing concrete mounded up to allow moisture run off.

Be sure to double check your posts are straight and plumb as your pouring concrete and a final check on completion, small changes can still be made however once the concrete sets changes range from difficult to impossible.

Allowing approx 2-5 days for the concrete to harden you will then be able to lower the house down onto the posts and tighten all the bolts.

Lifting and lowering

Time to wind the clock back and look at things a little differently. I have explained how to do a re-stump direct with minimal support however if we are lifting lowering or repositioning the building we need to go about things differently.

Counter balancing still playing a large role  as it does constraining or moving any heavy object with minimal effort. In the illustration or sketch following there is a network or grid formed from steel RSJ beams. 

Although the grid supports the building or load as I will refer it to, it still needs to be counterbalanced to keep the weight and material size at a manageable level and equally important the building needs to be kept on a flat plane and not drooping in places. This is important for a couple of reasons, the first of these is when it comes time to hanging the posts the building needs to fall into a 25-50mm clearance between the level point at which the post will sit and the height of the building while it supported. The second to avoid extreme pressure point where the weight of the load is transferred to a singular point.

For this reason you will need to do some pre thought and preparation. Internal walls, condensed building such as robes and cupboards will put extra weight in places and this needs to be considered.

Top view of the lifting frame

End view of the lifting frame

Usually what we call lifting steels are placed first. These lifting steels will run long ways under the building and out to the edges to the point where counterbalance is achieved when the cross steels shown in the sketch are lifted up under the house, roughly a metre in for an 8-9M wide building will be fairly close. They need to be as far out to the edges as possible without compromising the desired counterbalancing. The further out they are the lighter the lift but to far out and these benefits are very soon out weighed. That is if they are to far out to the edge they will bend and bow and if there to close to the centre extreme amounts of weight will be endured as you are attempting to lift the whole weight of the building from one point.

Once the frame is constructed it can be lifted up to the house supporting the lifting steel with frames and sties. The building can then be lifted off the post, the post removed and the house can be lifted or lowered in place.

There are at least two ways you can go about putting new stumps under at this point. If the building is in reasonable condition and the bearers can be drawn out on a plan accurately then you can set up forms and string lines and concrete the posts in with the building up higher out of the way, however my advice and certain the most forgiving methods is to restump in the same manner we earlier described in "Hanging by a thread".