A Build­ing Regs’ Guide to Build­ing Over Pub­lic Sew­ers

Build­ing con­trol of­fi­cer Paul Hymers looks at whether build­ing over a pub­lic sewer could scup­per your plans — and add to costs

Homebuilding & Renovating - - Contents - Paul Hymers Paul Hymers is a build­ing con­trol of­fi­cer and has writ­ten eight books on home im­prove­ment and build­ing homes.

There’s a cou­ple of ma­jor points to con­sider when it comes to Re­quire­ment H4 of the Build­ing Regs, par­tic­u­larly as this could put a stop to your de­vel­op­ment plans. The first re­gards the pres­ence of ex­ist­ing sew­ers, the sec­ond, con­nect­ing your new home to mains drainage.

The whole of Part H Drainage and Waste Dis­posal con­cerns it­self with foul wa­ter drainage, waste­water treat­ment sys­tems and cesspools, rain­wa­ter drainage, sep­a­rate sys­tems of drainage and solid waste stor­age, but for the pur­poses of this fea­ture, we’ll be fo­cus­ing on build­ing over or near sew­ers, and con­nect­ing to mains sew­ers.

How to Es­tab­lish Whether a Pub­lic Sewer Crosses Your Site This is one of the key ques­tions to an­swer be­fore build­ing a home — and should, in fact, be ad­dressed be­fore buy­ing your cho­sen plot. It could also im­pact if you’re ex­tend­ing your ex­ist­ing prop­erty.

If a pub­lic sewer crosses your site, you could have a ma­jor prob­lem, as most wa­ter au­thor­i­ties will not en­ter­tain an ap­pli­ca­tion to build over it. Just be­cause a plot has been granted plan­ning per­mis­sion, it doesn’t nec­es­sar­ily mean it can be built upon. A re­cent case was de­layed for eight months by a ma­jor sewer on site which re­quired a build over agree­ment, a sewer di­ver­sion and one cor­ner of the house near­est to the

sewer be­ing cut off and re­designed, all be­fore work could start on site. And if you’ve ever won­dered why you see the same plot rou­tinely pop up at auc­tion, a good place to start is by look­ing at the pub­lic sewer records. Some plots run be­neath the auc­tion ham­mer for years be­fore fi­nally (of­ten un­sus­pect­ing) buy­ers and their ar­chi­tects find a so­lu­tion to the prob­lem.

The wa­ter au­thor­i­ties tend

“When it comes to new builds, a pub­lic sewer cross­ing the site can be a ma­jor prob­lem”

to pre­fer a so­lu­tion that moves the build­ing away from the drain, but that of course means go­ing back to plan­ning with the new plans and this isn’t al­ways pos­si­ble or ac­cept­able.

It shouldn’t be too dif­fi­cult to find out whether you have a pub­lic sewer on your plot. The pub­lic sewer map records are in the pub­lic do­main — you can find them at your lo­cal author­ity of­fices, web­sites or li­braries. And of course, you can con­tact your lo­cal wa­ter author­ity and ask.

It’s a good idea to look out for man­holes when as­sess­ing a plot. Even if there are no man­holes pre­sent, a buried pipe may cross it none­the­less. This is re­ally where check­ing the sewer plans be­comes im­por­tant.

When You Might Need a ‘ Build Over’ Agree­ment You’ll need to ap­ply to your lo­cal wa­ter author­ity for a ‘ build over’ agree­ment if you are build­ing over or within 3m of a sewer serv­ing just one other prop­erty (known as a lat­eral drain). You don’t need your lo­cal wa­ter author­ity’s ap­proval if you’re build­ing out­side these dis­tances, and in the case of mi­nor sew­ers (de­fined as less than 3m deep and up to 225mm pipe di­am­e­ter), the Build­ing Reg­u­la­tions en­able the pro­tec­tive mea­sures to be agreed as part of the build­ing con­trol process with your ap­pointed lo­cal build­ing con­trol body.

Some wa­ter au­thor­i­ties have an agreed pro­to­col with the build­ing con­trol bod­ies in their re­gion to of­fer cus­tomers a faster, more ef­fi­cient ser­vice

when they come to build. The pro­to­col gives build­ing con­trol bod­ies the author­ity to ap­prove po­ten­tial build overs of mi­nor sew­ers on their be­half.

The Po­ten­tial Out­come of a ‘ Build Over’ Agree­ment

Of course, the prefer­able (and of­ten cheap­est) so­lu­tion for the self-builder is to lit­er­ally build over the sewer. How­ever, for the wa­ter au­thor­i­ties this is less than ideal — par­tic­u­larly if they need ac­cess to re­pair or main­tain it in the fu­ture. As such, it is more usual to ne­go­ti­ate a di­ver­sion de­sign for the sewer, which will take it around the build.

This can of­ten take time — some­times months. Wa­ter au­thor­i­ties are not in com­pe­ti­tion with any­one and have noth­ing to gain from the process be­yond try­ing to pro­tect their own drains. A de­tailed en­gi­neer­ing scheme must be pro­duced and ap­proved to their sat­is­fac­tion be­fore an agree­ment can be en­tered into. Even then, their own en­gi­neers will need to in­spect the di­ver­sion works on site as they take place.

In­vari­ably, if you are di­vert­ing a sewer, the drainage ma­te­ri­als need to be com­pat­i­ble with that of the ex­ist­ing sewer, which may be old. In this case, brick-built man­holes and clay pipes might be needed in­stead of PVCU ma­te­ri­als. Of course, the depth and the gra­di­ent of the sewer will de­ter­mine whether a di­ver­sion is pos­si­ble at all, since ex­tend­ing the run out and around the build length­ens the pipework be­tween two fixed points.

It’s in­ter­est­ing to see what hap­pens with the deeper tun­nel drains that are well be­neath any chance of be­ing af­fected di­rectly by tra­di­tional foun­da­tions of the new build. Of­ten many me­tres un­der­ground, these sew­ers are with­out hope of be­ing di­verted.

The older Vic­to­rian brick­built sew­ers may also be con­sid­ered vul­ner­a­ble and at risk from vi­bra­tion dam­age caused by me­chan­i­cal ex­ca­va­tion or vi­bra­tion of the ground above.

In these cases, a change in the de­sign of the foun­da­tions to a shal­low raft type may be needed. As well as dis­pers­ing the build­ing’s weight over the whole foot­print of the slab, rafts will also re­duce the dis­tur­bance to the ground dur­ing con­struc­tion.

What­ever the pro­posed so­lu­tion, a build over agree­ment is not guar­an­teed. Of­ten wa­ter au­thor­i­ties state on their web­sites that while they try to ac­com­mo­date build­ing over sew­ers for most ex­ten­sions and im­prove­ments,

that obli­ga­tion doesn’t ex­tend to new build­ings.

Con­nect­ing to Mains Sew­ers If you’re plan­ning to con­nect your new home to a pub­lic sewer, you’ll need the lo­cal wa­ter author­ity’s con­sent be­fore you go ahead. The wa­ter author­ity will need to check the con­nec­tion will work as planned, and that it won’t po­ten­tially cause prob­lems like sewer flood­ing or pol­lu­tion, al­though they will usu­ally have been con­sulted on these is­sues through the plan­ning process.

The fees vary from one author­ity to an­other, and also by the na­ture of the con­nec­tion pro­posed. For in­stance, for road con­nec­tions you’ll need to ap­ply to the high­way author­ity, to agree any mea­sures needed, such as traf­fic lights, per­mits, lane clo­sures and other is­sues. This can take months to be au­tho­rised, as well as adding to the cost of your work.

While you have a le­gal right to be able to con­nect to a pub­lic sewer, this doesn’t ap­ply to pri­vate sewer con­nec­tions out­side of your land. These de­pend on the agree­ment of the neigh­bour­ing landown­ers, and drainage ease­ments are es­sen­tial even when plan­ning per­mis­sion has been granted for a pri­vate sewer con­nec­tion out­side of your plot. As such, this will come at a cost.

Of­ten plan­ners get around this is­sue by im­pos­ing a Grampian con­di­tion. Neg­a­tively worded, these con­di­tions pro­hibit the de­vel­op­ment au­tho­rised by the plan­ning per­mis­sion or other as­pects linked to the plan­ning per­mis­sion (e.g. the oc­cu­pa­tion of the dwelling) un­til a spec­i­fied ac­tion has been taken, such as the agree­ment for con­nec­tion to drainage on neigh­bour­ing pri­vate land. Where this is not pos­si­ble, a sep­tic tank or sew­er­age treat­ment plant might be an al­ter­na­tive.

Sew­er­age Treat­ment Plants and Sep­tic Tanks

A fi­nal word about sew­er­age treat­ment plants and sep­tic tanks. Be­fore de­cid­ing on the type of stor­age or sewer treat­ment, the En­vi­ron­ment Agency should be con­sulted. In de­fined wa­ter aquifer zones, where rain­wa­ter is col­lected or rivers are close by, sep­tic tanks may be pro­hib­ited or re­stricted in size. Mini-treat­ment plants that cleanse the dis­charged waste­water may be nec­es­sary. In heavy soils, like clay, the ir­ri­ga­tion drainage from sep­tic tanks may also be in­ef­fec­tual.

Next month : Build­ing Regs Guide to Wa­ter Ef­fi­ciency De­sign (Part G) Ex­plained

Tra­di­tional Man­hole

A tra­di­tional one brick thick man­hole con­structed from semi-en­gi­neer­ing bricks is usu­ally re­quired for new pub­lic sewer in­spec­tion cham­bers, rather than the PVCU pre­fab­ri­cated types.

© Crown Copy­right

Use­ful, but Not Al­ways Ac­cu­rate

The pub­lic sewer maps can show pipe runs, di­am­e­ters, in­spec­tion cham­bers, in­vert lev­els and cover lev­els for both foul and sur­face wa­ter pub­lic sew­ers — but not al­ways ac­cu­rately, which is why you should al­ways in­ves­ti­gate on site.

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