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transform@ensoul.co.uk 44 (0)20 3637 0700Create. Transform. Inspire.The London Guide toUnder Garden BasementsIncludes: 5 Great reasons to gounder your garden vs under your housewith your basement projectUpdated for 2017
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700ContentsIntroduction: The London Guide to Under Garden Basements35 Great reasons to go under your garden vs under your housewith your basement project4Step 1: Understanding the planning rules5Step 2: Ensuring Value6Step 3: Surveys7Step 4: Architectural design & space planning8Step 5: Neighbour Support9Step 6: Planning Application10Step 7: Technical and structural design11Step 8: Engaging a basement contractor to build your basement13Step 9: Interior Design16Step 10: Fit Out Contract17Article summary and conclusions182
transform@ensoul.co.uk 44 (0)20 3637 0700Create. Transform. Inspire.The London Guide toUnder Garden BasementsFor those with a big garden or driveway who are thinking about a houseextension, we recommend you consider an under garden basement orunder driveway basement.Mike Lander,Project Manager &Programme DirectorDig deep to get a high ceiling, put in light wells and roof lights to get anincredible space that feels just as good, if not better than youraccommodation upstairs.These are some of the rooms and types of accommodation that we areseeing under garden basements being used for: cinema roomkids playroomgames roomwine cellar and wine tasting roomcigar room / walk-in humidor gymsaunaswimming poolspamassage roomsanctuary nanny, granny and teenage flatsbarnightclub dance floorbowling alleyrecording studioluxury car parkInterested?This guide will explain how Ensoul Architectural Design can take you all the way from initial interest, through theplanning application process and then into construction and handover.Under garden basements add significant value to your property; Ensoul has delivered more than 200% returnon investment for under garden basements in terms of the uplift in property valuation versus basement cost forseveral clients. But aside from adding serious amounts of floor space and value, here are 5 great reasons to gounder your garden instead, or as well as under your house.Step by step guideWhat follows is a comprehensive, step-by-step guide to under garden basements from first concept through tofinal handover back to you as the client. This same sequence equally applies to under-house as well asunder-garden basements although some of the emphasis/detail will be different in some of the steps.3
5 Great reasonsto go under your garden vs under your housewith your basement project12Brighter and lighterFresherBy building a basement under a gardenor driveway, we can design-in walk-onroof lights, front and rear light wells andterraces to maximise the effect of light inyour basement.With light wells and lower terraces youcan throw open the doors to bringin fresh air and, with some plantingand furniture you can enjoy a smallsubterranean garden.34QuickerBiggerIf you have good side access to yourgarden, getting efficient excavation andconstruction equipmenton-site could save you considerable timeand hassle on your construction.If you are fortunate enough to have along or wide garden, you can createa large basement footprint as analternative, or in addition to, an underhouse basement.5Lower impact to you and your neighboursUnder garden basements can be quicker to build with fewer structural risks making thempotentially cheaper to build. This isn’t always the case, but Ensoul can help you assess thisduring the feasibility stage of your basement project.transform@ensoul.co.uk 44 (0)20 3637 07004
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700Planning restrictions1Understandingthe planningrulesEvery planning office has a different policy regardingwhat you can and can’t do with under gardenbasements and basements generally in their borough.It’s therefore important that you investigate the latestbasement policy and guidance of your local authorityat the very start so you know what kind of basement isfeasible, the requirements attached to the applicationand any design or cost implications. For example: Wandsworth basement policy recommends that itwould be good practice to retain a depth of at least50% of the back garden. Merton basement policy stipulates not to exceed50% of either the front, rear or side gardenof the property. Royal Borough of Kensington & Chelsea basementpolicy limits the extent of basement excavation tono more than half the garden and the depthof a single storey only. And Westminster’s new basement policyhas introduced a levy from 1 September 2016for a subterranean squad of “basement nuisancebusters’ – charged with overseeing and controllingtraffic impact, stricter working hours andcomplaints. It’s the first of its kind in the countryand assumed to be picked up by otherboroughs eventually.Conservation area restrictionsIf this is applicable, you will need to ascertainany additional restrictions placed on a basementdevelopment in your area.5
transform@ensoul.co.ukCreate. Transform. Inspire.2EnsuringValue 44 (0)20 3637 0700You need to conduct desk research and talk with localestate agents to establish what your newly proposedbasement will add in terms of additional pounds persquare metre. You can then ensure that the cost tovalue ratio is in balance and that you get a great returnon investment.We have seen the ratio of property value per squaremetre to build cost per square metre at 2:1 or more insome cases.The keys to maximising valueare size, height, lightand fit-out.6
transform@ensoul.co.ukCreate. Transform. Inspire.3Surveys 44 (0)20 3637 0700Before you start to think about the design andplanning application, you will need to get surveysdone to inform the basement technical design andpossibly to be included in your application: Geo-technical survey - this reports on the soilstructure down to the depth you are digging andany likely issues regarding the height of thewater table. Drains’ survey to ascertain where the drainsrun around/under your house and gardento understand the impact of the basementconstruction. Depending on where the drains run,a separate “build-over” agreement may be requiredfrom your water utility provider. Topographical survey to get accurate dimensions ofthe site. Arboricultural survey to investigate trees inyours and your neighbours’ gardens to see whatimpact a basement dig may have on the health ofany trees. Also, as part of this step, identify any thatfall under a Tree Preservation Order.7
transform@ensoul.co.ukCreate. Transform. Inspire.4Architecturaldesign & spaceplanning 44 (0)20 3637 0700Once armed with local authority policy, the necessarysurvey results and an outline budget estimate, you willneed to design your basement space plan which willinclude: How big and what shape it will be How you propose to connect your new basementto your existing house What’s the best space plan and room lay-out A high level interior design plan and furniture layout so that you know the architectural design is inperfect harmony with the interior plan Where to put services i.e. drains, electric runs,ventilation, etc. Access and exit points including compliance withbuilding regulations Roof lights and light wells to provide lots of naturallight and ensure a high quality living space A garden lay-out that will go back on top of yournew basement8
transform@ensoul.co.ukCreate. Transform. Inspire.5 44 (0)20 3637 0700At this stage and definitely pre-planning application,we recommend making the time to book 1:1 meetingswith your close neighbours to talk about your plansover a coffee or a glass of wine. Ensoul can help tocreate a presentation pack for you and can attend if it’shelpful to answer technical and build questions.The main things to communicate are:NeighbourSupport Explain why you’re wanting to create your newspace and what it will mean to you / your family.Neighbours are far more supportive if theyunderstand that you need more space for musicpractice with contained noise levels, or space for alive-in nanny so that you can go back to work, etc. Provide them with a top-level overview of theproposed basement size and design. Go through timings with them so they canunderstand the duration of works and impact tothem. Explain that it is being professionally designed, builtand managed to quash any fears about “cowboys”potentially collapsing your houses. Make a small gesture to them e.g. pay for a windowcleaner once a month during works. The goodwillwill go a long way and in the scheme of things, thecost is minimal. Critically, get any concerns or questions answeredthere and then, or written down so that they aredealt with immediately or if not there and then,before planning. This will prevent potentialcomplaints or open comments on your localplanning website when you file your application.9
transform@ensoul.co.ukCreate. Transform. Inspire.6PlanningApplication 44 (0)20 3637 0700Next, finalise your plans, write the necessary contentand file your planning application which will take upto 8 weeks from acknowledged receipt by your localplanning office.Typically, your assigned planning officer will wantto visit and will have some questions that needanswering and are likely to indicate some conditionsthat may be required to give planning consent. Ensoulcan handle all of this on your behalf through toconclusion and result.We ensure that all thedocumentation required tosupport your application is inplace before submission.10
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700Structural design and calculations:7Technical andstructuraldesignA structural engineer now needs to be appointed todecide and detail the best way to design, supportand build your basement shell and core. The ‘shell andcore’ is fundamentally the concrete and reinforcedsteel structure in the ground. The engineer’s designwill factor in all survey information available as wellas your project timescales and budget constraints.The resulting piece of work is a series of drawingsand calculations which identify the constructionsequencing, materials, steelwork, under-pinningand/or piling details, party wall detailing and CDM(Construction Design & Management) requirements.The structural design is required before the Party WallAgreement process starts as any appointed surveyorwill want to review these as part of your Award.Waterproofing design:How the basement structure is designed will alsodetermine the best waterproofing system design. Onthe assumption that your basement is structurallysound, waterproofing it is the next most importantaspect of your build. A leaking basement createsenormous stress and is an incredibly difficult problemto solve. Because water travels, it can be very difficultand in some cases, impossible to find the entrypoint. So, you must ensure you have the very bestwaterproofing experts designing your basement fromthe start. The way the waterproofing system is designedalso has implications for the insurances/guarantees youwill need to put in place.Some of the larger specialist basement constructioncompanies have extensive skills in this domain inhouse. However, it is a highly specialist and skilledarea and when using smaller firms, we recommendengaging an experienced waterproofing designconsultant to work as part of the design team. If youwould like to find one, here’s a great place start yoursearch: http://www.thebswa.plus.com/Architectural design:Based on the Planning Application drawings, the nextlevel of detail can now be developed.11
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700We recommend that you think about your basementworks as two distinct projects:8Engaging abasementcontractorto build yourbasement Basement shell and core: this is the creation ofyour waterproofed, concrete structure in theground. A specialist contractor, as opposed to ageneral building contractor, is required for thisbasement construction stage. Make sure that youare contracting the actual contractor that is goingto conduct these works – not a firm that is going tosubcontract these specialist works andsimply put margin on it. Basement fit-out: this element is focused aroundthe interior finishes and includes for example, wallformation, plastering, flooring, lighting and electrics,plumbing, decoration, joinery, etc. Most basementcontractors only focus on delivering shell andcore packages and are not interested, or sufficientlyexperienced, in delivering fit-out work.The most efficient way of constructing your basementis to get your Shell and Core contracted first as adetailed package of works with a fixed price. This way,you can get your project up and running and whilstyour basement is being dug out, you can be designingthe interior of your basement (either yourself or witha professional), and selecting all the internal finishes.Once this work is done, you can get an accurate scopeand budget put together by your design firm and/orfit-out contractors.There are a small number of high quality buildingfirms that can take on both the “shell and core” andthe fit out, however, predominantly, they are differentcompanies with very different skills.12
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700Contracting the shell and core:Once in receipt of the architectural plans and structuralengineer’s drawings and calculations, you will needa detailed scope of works ready to discuss with prevetted basement contractors. There are two main typesof contract we use: JCT Design and Build Contract (watertightshell and core)This provides a single point of accountability for allelements of your basement shell and core designand build including: Structural and temporary works design Waterproofing design and drainage Basement shell and core build External glazing JCT Intermediate with CDP (ContractorsDesign Portion) and minor works contractsThese contracts are typically used when it makessense to break out one or more elements of thebasement design and/or build to specialist 3rdparties. This decision may be taken if the preferredbasement contractor has a lack of expertise /experience with a particular element, or becausethere is a significant cost variation between havingit all under one roof vs taking some elements out ofscope. For instance: The structural design could be contractedwith an independent structural engineer The waterproofing installation could becontracted with a specialist waterproofingprofessional.13
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700Guarantees and insurances:We strongly advise that you take expert advice onguarantees and insurances.If the unthinkable happens, your basement leaks, andyour contactor has gone bust, what happens next?Who are you going to try and claim against? Or, if youdecide to sell the property and the buyer asks whatguarantees are in place, how are you going to give theirconveyancing solicitors comfort that all the guaranteesare robust.The fundamental elements to consider include: Builder company guarantees Waterproofing guarantees (design, product andinstaller) Insurance backed guarantees Latent defects insurance Building’s renovations insurance (Joint Names)InspectionsDuring the build, an approved Building ControlInspector will need to be appointed to oversee theconstruction work and sign off that the structureconforms to Building Regulations. This will requirevisits at key stages which will be co-ordinated by yourbasement contractor.Excavation and building theconcrete boxNow the works can start and the next phase beginswhich is managing the basement contractor on-siteto deliver against the design details that have beendeveloped without variation. This deserves an article inits own right rather than describing the extensive detailhere.14
transform@ensoul.co.ukCreate. Transform. Inspire.9InteriorDesign 44 (0)20 3637 0700If you have not done your interior design beforehand,you can do so once your basement contractor startsworks on the shell and core as this element will take afew months before completion.Your basement interior will need designing and allfixtures and fittings will need specifying e.g. roof lights,light wells, windows, external and internal doors,staircase, floor and wall finishes, sanitary ware, tiles,paint colours, AV and IT networks, HVAC, heating,ventilation, air conditioning), security, light fittings,furniture selections, etc.For a beautiful result and efficient flow of works, hirean interior design company to put together a cohesivescheme and to recommend full product selections toyou.You would be amazed at how many products andfinishes you will need to pick and agree, so if you canafford to bring in help, we recommend you do so.If you’re bringing in a designer, make sure they canhandle the technical design such as lighting plans,floor make-ups, glazing details, etc. as well as the ‘prettystuff’. It also pays to ensure that your design teamcan deliver a technical CAD package of drawings anddetailed schedules so that you can see exactly whatyou are getting and sign it off; and so that the builderknows exactly what to cost and then build to with noambiguity.15
transform@ensoul.co.ukCreate. Transform. Inspire.10Fit OutContract 44 (0)20 3637 0700Once you have your agreed fit-out package of drawingsand schedules, it can be sent out to fit-out contractorsto provide a fixed price quote. You or your designer willalso need to get all of the products quoted as wellby all the various suppliers once you once you havechosen everything to create the fixed price budget.By selecting everything before the fit-out starts, youcan make sure that your basement interior design iswell thought through and cohesive and that you aregetting an accurate fixed price quote from builderswith everything detailed and included.It also means that you can fix a price at the start witha contractor and ensure that when they start works,they have all the information they need to deliver theprogramme of works.16
transform@ensoul.co.ukCreate. Transform. Inspire. 44 (0)20 3637 0700Article summary and conclusionsAs you will see from this article, there is a considerableamount of detail to be managed, third party serviceproviders to co-ordinate and tendering processesto go through. Think seriously about getting anindependent Project Manager with experience inbasement construction. We’ve written an article onthe benefits of professional project management anddefined the key areas of responsibility / scope of worksthat one should be contracted to deliver against.In conclusion, under garden basements add a fantasticamount of living space and can significantly improveyour quality of life. Our advice to anyone embarking ona basement project is to:One of the common questions we get asked is “Howlong will my basement take to build once contractorsstart work?” For an average basement of say, 100sqmand one storey deep, allow approximately 9-11months which breaks down broadly as follows: Ensure that you bring in experienced and capablecontractors who know how to safely constructbasements and make sure they’re watertight.Beware of going cheap. Watertight shell and core 5-7 months: Site set up Excavation, temporary works, dewatering,underpinning/piling Floor slab and sump pumps Staircase and roof slab Waterproofing and drainage Underfloor heating and screeding Rooflights and lightwell glazing Testing & certification Site demobilisation Engage an experienced design team at the conceptstage to ensure you optimise the space design,room lay-outs and quality of light to deliver a welldesigned, high quality living space. Bring in expert knowledge to write and packageup your contracts with the builders and tomake sure that you have the right insurances,guarantees and warranties in place. Seriously consider getting a professional projectmanager who is experienced in basement builds tomanage all contractors and third partyprofessional firms from the initial design stage rightthrough to hand-over. Fit-out: depends on complexity of build/finishes butallow 3-4 months Landscaping (if it’s an under garden): depends oncomplexity of design but allow 1 month (this canoccur in parallel with the interior fit-out) Furniture & soft furnishings: subject to order datesand lead timesRelated ReadingHow much does a basement cost?As the trend for London basementconstruction continues to soar, the mostpopular question we get asked at Ensoul is“How much does a basement cost?”Read more on our blog17
transform@ensoul.co.uk 44 (0)20 3637 0700Create. Transform. Inspire.Create. Transform. Inspire.Want to find out more or get started?Call Us 44 (0)20 3637 0700Email Ustransform@ensoul.co.uk18
Webwww.ensoul.co.ukPhone 44 (0)20 3637 0700 2017 Ensoul Interior Architecture, LondonEmailtransform@ensoul.co.uk
structural design 7 Structural design and calculations: A structural engineer now needs to be appointed to decide and detail the best way to design, support and build your basement shell and core. The ‘shell and core’ is fundamentally the concrete and reinforced steel struct
