Are you trying to choose the right solution for waste from an annex?
Building a small out-house or annex in your garden is a great way to add value to your property. However, the question of what to do with the sewage waste is one that often arises
I often speak to contractors facing the question of what to do with the sewage from an annex. Nine times out of ten the first thought is to install a small septic tank or treatment system; however this is not always the best option. In this article, I explain the different options available to you to help you make a good long-term decision.
You have 4 options for treating sewage from an annex, these are:
The above options are all valid options, but they must be considered carefully. The intended use of the annex also plays a roll in the choice made. Let’s look at the options in more detail.
This isn’t necessarily a bad option however the drainage field must conform to British regulations. You cannot use soakaway crates as they provide no “post tank” treatment of the water, therefore you are likely to pollute the ground.
The drainage field must be designed and constructed correctly as detailed in "Part H" of building regulations.
You might be wondering if the tank will smell. It is a good question; intermittent flows of water are likely to cause the septic tank to smell. For this reason, I would only suggest this if the annex is intended to be used frequently.
Sewage treatment plants treat water to a higher level than a septic tank, and therefore are allowed to release water into a ditch or stream under the general binding rules (although you might need a permit if the ditch doesn’t have water flowing all year round).
Whilst treatment plants are generally permitted for discharge to a ditch or stream, you still have an obligation for the system to “not pollute”.
Will a treatment plant work for an annex? The answer is yes with the proviso that there is a regular flow of water to the treatment plant. If the annex is only used for guests, it is unlikely that there will be enough regular waste for bacterial growth and therefore this solution should be avoided in most cases.
It is only recommended to use a treatment plant for an annex if flow is regular, and even then I would use a system that can deal with low flows and higher concentrations like the Solido Smart
On a side note, the Solido smart is only capable of treating low volumes of water if it is programmed to do so, I would recommend changing to one treatment cycle a day in this situation.
It is common for people to consider a cesspit (which is just a holding tank). With very low flows, one toilet flush a week for example, this might be a good option. However, smell should be considered and as with all of the other previous options, you will have to get the tank emptied and therefore consideration as to the location of the tank becomes important. Most emptying tankers only have a 30m reach to empty the tank, so keep this in mind.
This option often gets disregarded very quickly due to distance from the main building. However, in my opinion it is the best option. A small pump chamber installed in the ground outside the annex will easily be able to pump the water 50 or more metres. The pump will be silent, and most modern pumps do not need to churn up the waste like a “saniflow” system. A “Vortex” pump allows all the solids to pass through the pump which greatly reduces the risk of blockages.
With this solution, there is no need to consider emptying the tank, no risk of pollution, no smell and no noise. It is often cheaper to purchase, costing as little as £800-£1000 for a good pump and chamber. Costs will rise if you choose a twin pump system, which in most cases of an annex, is unnecessary. I would however purchase an alarm to inform you in the event the pump stops working. An alarm will cost around £200.
If the main house has a sewage treatment pant then consideration should be made as to whether or not the treatment plant can cope with additional flow.
A pump station is the most viable option for dealing with waste from an annex and should be considered first and foremost when deciding upon a sewage solution. Ensuring the tank and pump is sized correctly is important, therefore speaking to a specialist is recommended rather than just going online and buying one.
Want to discuss if a pump station can work for you? Fill in the contact form and I will be happy to talk through your project and assess the feasibility of pumping vs treating your sewage.
If you require a solution for your outbuilding or annex, feel free to leave your details below and i will contact you to discus your options: