The best way to install starter strip on old houses or even new houses is to use a self leveling laser level. These tools are expensive, but usually can be found for rent at your local tool rental or Home Depot. Setup the laser and shoot each corner of the house. Determine the lowest point which siding must be installed and use that as your reference point. If necessary you can then add furring strips to the walls to fasten starter strip to and then begin installing siding.
You can use the PVC clear tubing 1/4"-3/8" 100 feet long or less 50 works fill it up with water you can add Color in so you can see better to the water and using as a water level you need to have two people for doing that one is staying on one corner and other go to the other corner soon as water stop moving in tubing you need to mark the point with pencil and go around house then you will find your lower corner where do you have to start your siding.
Shouldn’t be that expensive at Home Depot
There are two ways you may set the level for the starter strip. The first way using a laser level is described below. Due to the cost unless you have use for such a tool it is probably not the most cost effective route for a one time project. In that case I recommend purchasing a spool of lashing string and a small hook on level. The total out of pocket for these two items is less than $10. Attach one end of the string to the corner of the wall you wish to install a starter strip, next hook on the hanging level and walk the string to the other corner, now observe the level and adjust the string until it’s level. Secure the end to the house and set the starterstrips against this mark.
Install the starter strip with the natural angle of repose. If the home has settled, it would be a good idea to make sure it is stable and doesn’t continue to drop any further, speak with your local engineering office for more info. For a more visually pleasing finished siding job, install the siding with the current slope of the home. If the house isn’t level, and you install the siding level it will disturb the natural visual flow by having planks trimmed down at angles to fit square at the edges or if it is sheet siding you will have “steps” at every joint. (even if they are trimmed flush with each other). Go with the flow of the house and all will be well.
the problem with everyone’s laser level ideas and explaining how level the siding should be is there opinions and i respect it my opinion is this, if the house settled i found out a lot of times so did the windows, if you are good at siding, you can see if something is off by looking at it, always start at the lowest point on the house, # 1 the first couple low panels can afford to be off a little what you don’t want is by the time you get to eye level you don’t want a crooked panel especially visible, eye level is usual right at the windows too if you made all your panels level by the time you get the the stool caps you will have level siding yes but now your windows will look horrible and visible, i would make small adjustments from the low point with the starter strip to the windows make adjustments with your stool caps and the siding it wont be 100% level yet but it won’t look crooked vinyl can stretch a little bit don’t yank on it just little adjustments to look level once you have adjusted to look level at the windows you should be able to adjust all your panels in between the windows and the rest of the way up to go back level, make small adjustments with corner posts if you have to lower them a little bit and bend your own starter strip because the prefabbed starter ain’t wide enough , we can talk about tricks of the trade all day
First you should install a foundation wrap (L flashing made from coil stock the same color as the siding) around the entire house to prevent moisture from wicking up into the wall sheathing. Then find your lowest point of the home. Pull a measurement down from the soffit. Pull this same measurement on each corner. This way you will always end level with your soffit. If it is only 1 to 2 inches out of level this should not matter because most starter strip is 3 1/2". You will still be able to attach it to the wall sheathing. It will just be 1 to 2 inches below the wall sheathing on the high points. Which you want 1/2" anyway.