Terms of service

Effective date: 24 September 2026 · Last updated: 4 October 2026

1. About these terms

1.1 These terms govern your use of Offset, the compensatory heat-loss and area-weighted U-value calculation service at offsetapp.co.uk and app.offsetapp.co.uk ("Offset", "the service").

1.2 Offset is provided by Murdo McDermid, a sole trader trading as Offset App, of Tribe Porty, 19 Windsor Place, Edinburgh, EH15 2AJ ("we", "us"). You can contact us at support@offsetapp.co.uk.

1.3 By creating an account or using the service you agree to these terms. If you are using Offset on behalf of a practice or company, you confirm you have authority to bind it, and "you" includes that organisation.

2. Your account

2.1 You must be at least 18 and provide accurate details. Keep your login credentials confidential and tell us promptly if you think your account has been compromised. You are responsible for activity under your account.

2.2 Practices and members. Offset is organised around practices. The person who creates a practice is its owner. The owner controls the practice's plan, profile and membership, can invite people to join, and is responsible for the conduct of the people they invite.

2.3 Calculations saved within a practice are shared with, and can be viewed and edited by, that practice's members. If a member leaves, the calculations already saved in the practice remain with the practice.

3. What Offset is — and is not

3.1 Offset is a calculation aid. It applies published methods and notional U-values to the figures you enter and produces a comparison of proposed against notional heat loss. It is a working tool for competent professionals. It is not a verified or approved compliance certificate, and its output is not professional, legal or building-control advice.

3.2 You are responsible for your inputs and for the result you rely on. The output is only as good as the areas, U-values and product data entered. Before using any result in a building warrant, planning or building-regulations application, you must check the figures and method against the current official documents that apply on the relevant date (for example the Scottish Technical Handbooks, Approved Document L, and the Northern Ireland Technical Booklets), and against the manufacturer's current product documentation.

3.3 Regulations change. We aim to keep the built-in tables and methods current, but we do not guarantee that they are complete, error-free or up to date. Some tables cover editions that are not yet in force, and some non-domestic figures may be unpopulated for particular nations; where the service says so, enter your own reference figures.

3.4 The final decision on whether a design complies, and on what is submitted, is yours and any verifier's or building control body's — not Offset's.

4. Plans, billing and cancellation

4.1 Plans and prices. Offset is offered on a free plan and on paid plans. As at 29 September 2026 they are:

The price shown to you at checkout is the price that applies to the billing period you are buying, and prices may change for later periods as set out in 4.3. We may change the free plan and its limits from time to time.

4.2 Payment. Except for Enterprise plans (see 4.8), paid plans are billed in advance, monthly or annually as you choose, by card through our payment processor, Stripe. We do not see or store your full card details. We are not registered for VAT, so no VAT is charged. If we become VAT-registered, we will tell you before VAT is added to your subscription. Billing is per practice, not per person.

4.3 Renewal. Paid plans renew automatically at the end of each billing period at the then-current price until cancelled. We will tell you in advance of any price increase, and it will apply from your next renewal.

4.4 Cancelling. You can cancel at any time from your account (via the billing portal). Cancellation takes effect at the end of the billing period you have already paid for, and you keep paid features until then. We do not give refunds because you have changed your mind or stopped using Offset part-way through a billing period. We will give a refund, or other remedy the law provides, if the service is faulty or not as described, and consumers also have the cancellation right in 4.5.

4.5 Consumers: your right to cancel. If you are an individual using Offset wholly or mainly outside your trade, business, craft or profession (for example, a self-builder), you have the right to cancel your subscription within 14 days without giving any reason. The cancellation period ends 14 days after the day you subscribe. To cancel, tell us of your decision by a clear statement, for example an email to support@offsetapp.co.uk or a letter to the address in 1.2. You may use the model cancellation form in the Appendix, but you don't have to. (Cancelling from the billing portal stops future payments, but please also tell us you are using this right so we can refund you.) To meet the deadline, it is enough to send your message before the 14 days have passed. We will acknowledge it by email. If you cancel, we will refund everything you have paid us for the subscription, without undue delay and no later than 14 days after the day you tell us, using the same payment method you used unless you expressly agree otherwise. You will not be charged any fees for the refund. Your access to paid features ends when you cancel. Nothing in these terms limits your statutory rights.

4.6 Changing or ending a paid plan. If your plan changes to one with lower limits, the lower limits apply going forward. We will not delete calculations you have already saved because of a downgrade: you can keep viewing, editing and printing all of them. But you will not be able to save a new calculation until the number you have saved is below your plan's limit (or you upgrade) — so if you have 6 saved on the Free plan, which allows 4, you would need to delete down to 3 before you could save another. The same goes for team members: if your plan's member limit falls below the number of people in your practice, the practice keeps its owner and its earliest-joined members up to the new limit, and the others lose access to that practice (their own accounts and the calculations already saved in the practice are not deleted). If you upgrade again, you can invite them back.

4.7 Failed payments. If a payment fails we may retry it and may downgrade the practice to the free plan if it stays unpaid.

4.8 Enterprise plans. Enterprise plans are agreed individually in writing. We can bill them by invoice, payable within 30 days of the invoice date, and will quote your purchase-order number on our invoices if you give us one. We can also help you complete security and compliance questionnaires.

4.9 Refer a friend. Each account has a personal referral link, shown under "Refer a friend" in the app.

(a) If someone who does not already have an Offset account creates one through your link, the first paid plan they take out for a practice they own starts with a 30-day free trial. Their card details are taken at checkout, and the first payment is taken when the trial ends unless they cancel before then.

(b) Once that first payment has been taken, the practice you own receives account credit worth one month of its plan at the monthly price, or one month of the Individual plan if it is on the free plan. The credit comes off your next bill, or your first bill if you subscribe later. It has no cash value, cannot be transferred, and is not refunded if you cancel.

(c) You can receive credit for up to 12 referrals in any 12-month period. People who sign up through your link after that still get their free trial.

(d) Only share your link with people you know. You must not send it in unsolicited marketing emails or messages, post it anywhere as spam, or create accounts to refer yourself. We may withhold or reverse credit gained through misuse.

(e) We may change or end the referral scheme at any time. This does not affect credit you have already received.

5. Your content and the reports you produce

5.1 You keep ownership of the calculations, project details, notes, logos and other material you put into Offset ("your content"). You give us a limited licence to store, process and display it, and to keep it secure, solely to run and improve the service for you.

5.2 Reports. You may print and export reports for your own professional use and to give to clients, verifiers and authorities. Printed reports may carry an "Created using Offset" footer, and, on paid plans, your own practice logo instead of ours.

5.3 You are responsible for your content: you confirm you have the right to use it, including any logo you upload, and that it does not infringe anyone else's rights or contain anything unlawful.

6. Acceptable use

6.1 Do not: misuse or attempt to break, probe or overload the service; access another practice's data; share your login with people outside your practice or use one paid seat for several people; reverse engineer the service; use it to build a competing product; or use it for anything unlawful.

6.2 The product library. The rooflight product library is available to signed-in users. It is a database we have compiled and verified from manufacturers' published literature through substantial investment, and we own the database right in it. You may not scrape, bulk-extract, republish or resell it, or use it to build a competing database. We keep records of access to the library to protect it (see our Privacy Policy).

6.3 We may remove content or restrict access where these rules are broken.

7. Manufacturer names, logos and data

7.1 Product names, logos and marks of third-party manufacturers (including VELUX, Korniche, The Rooflight Co. and FAKRO) belong to their respective owners. Offset is independent and is not affiliated with, endorsed by or sponsored by any of them.

7.2 Product dimensions and U-values in the library are reproduced from each manufacturer's own published literature. They are provided for convenience and may be incomplete, superseded or change without notice. Always confirm them against the manufacturer's current documentation before relying on them.

8. Our intellectual property

8.1 Offset, its software, design, text, tables, layouts and branding belong to us or our licensors. Apart from the right to use the service under these terms, we grant you no ownership or other rights in them.

9. Feedback, bug reports and requests

9.1 If you send us feedback, bug reports or requests (for example through "Report a bug" or "Request a manufacturer / range"), you agree we may use them freely, without payment or credit, to improve the service. We may contact you at the email address you give us about your report.

10. Availability and changes

10.1 We work to keep Offset available and accurate, but we provide it as is and as available. We do not guarantee uninterrupted or error-free operation, and we may carry out maintenance, change features or discontinue parts of the service. We will give reasonable notice of changes that materially reduce what a paid plan includes.

10.2 Keep your own copies. We do not guarantee that your content will be backed up or that it can be recovered if it is lost, so please print or save as PDF any report you rely on, and keep your own records of anything important — particularly anything submitted with a building warrant or application.

10.3 Events beyond our control. We are not responsible for any failure or delay in providing Offset caused by events beyond our reasonable control, such as a failure of our hosting, database, email or payment providers, a wider internet or power outage, or a cyber-attack we could not reasonably have prevented. We will tell you if this happens and do what we reasonably can to restore the service.

11. Suspension and ending your account

11.1 You may stop using Offset at any time.

11.2 We may suspend or end access if you breach these terms, if a payment remains unpaid, if needed to protect the service or other users, or if we stop providing the service (in which case we will give reasonable notice and, for paid plans, refund any prepaid period we cannot honour).

11.3 To delete your account and its data, email support@offsetapp.co.uk. We will delete your account and remove your content within 30 days of your request, except where we must keep information for legal or accounting reasons.

12. Liability

12.1 Nothing in these terms limits or excludes liability that cannot lawfully be limited or excluded, including liability for death or personal injury caused by negligence, for fraud or fraudulent misrepresentation, or your statutory rights as a consumer.

12.2 Subject to 12.1, and because Offset is a calculation aid whose results you must verify (section 3): we are not liable for any loss arising from your reliance on a result, including a building warrant, planning or building-regulations application being refused, delayed or needing rework, or any design, construction or remedial cost that follows.

12.3 Subject to 12.1, we are not liable for indirect or consequential loss, or for loss of profit, revenue, business, goodwill or data, however arising, whether in contract, delict (including negligence), breach of statutory duty or otherwise.

12.4 Subject to 12.1, our total liability to you arising out of or in connection with the service, whether in contract, delict (including negligence), breach of statutory duty or otherwise, is limited to the amount you paid us for the service in the 12 months before the claim arose.

12.5 If you are a business, all warranties, conditions and terms implied by law are excluded to the fullest extent permitted.

12.6 Claims by your clients (business customers only). If you use Offset in the course of your business, you will reimburse us for any claim brought against us by a third party (for example, your client, a building owner or a contractor) arising from their reliance on a calculation or report you produced with Offset, or from content you uploaded, together with our reasonable costs of dealing with it, except to the extent the claim results from our own breach of these terms. This does not apply to consumers.

13. Your data and privacy

13.1 How we collect and use personal information about you, as an account holder, is set out in our Privacy Policy. Your calculations are stored on servers in the EU (Frankfurt); email is sent through our email provider and payments are processed by Stripe.

13.2 Confidentiality. We treat your content, including your calculations, project details and notes, as confidential. We will not disclose it to anyone except our service providers who need it to run Offset (13.3), or where the law requires us to.

13.3 Your clients' personal data (business customers). Calculations can include personal data about your own clients, such as site addresses. For that data you are the controller and we act as your processor under the UK GDPR, and this section 13.3 is the contract between us that Article 28 of the UK GDPR requires. We process that data to provide Offset to you: we store it, show it to you and the other members of your practice, and use it to produce the reports you ask for. We do this for as long as your account is open, and then until the data is deleted under 11.3. We will:

• process it only on your documented instructions, which are these terms and the way you choose to use Offset, including when it comes to transferring it outside the UK, unless the law requires us to do something else. If it does, we will tell you before we do it, unless the law prevents us from telling you;
• tell you straight away if we think an instruction from you breaks data protection law;
• make sure anyone at Offset who can access it is bound by confidentiality;
• keep appropriate technical and organisational security measures in place;
• use only the sub-processors needed to run the service, and tell you before adding or replacing one so you can object. These are currently Supabase, which stores calculations in the EU (Frankfurt); and, only if you include client details in a bug report, manufacturer request or support email, Resend, which delivers those messages to us, and IONOS, which hosts our support inbox. Netlify, which hosts the app, and Stripe, which handles payments, do not receive calculation data. Where a sub-processor transfers personal data outside the UK, it does so under safeguards recognised under UK data protection law, as described in our Privacy Policy. Each sub-processor is bound by a contract that imposes the same data protection obligations as this section, and we remain fully liable to you for how they meet those obligations;
• tell you without undue delay if we become aware of a personal data breach affecting it;
• help you respond to requests from individuals exercising their data protection rights, and help you meet your own obligations on security, breach notification, impact assessments and consulting the Information Commissioner, as far as reasonably possible given the nature of the service and the information available to us;
• when your account ends, return the data to you or delete it, as you choose, and delete any remaining copies unless the law requires us to keep them. You can keep your own copy at any time by printing or saving your reports as PDFs. If you would also like a copy of the underlying data, ask us before your account is deleted and we will send it to you in a commonly used format. Otherwise we will delete it under 11.3; and
• give you the information reasonably needed to show we meet these obligations, and allow for and contribute to audits, including inspections, by you or an auditor you appoint. We will first try to answer any audit through documents. Any audit must be on at least 30 days' notice, during normal working hours, at your cost, under a duty of confidentiality, and no more than once a year, unless a personal data breach or the Information Commissioner requires otherwise.

You confirm that you have a lawful basis for entering your clients' personal data into Offset.

14. Changes to these terms

14.1 We may update these terms, for example to reflect new features or changes in the law. We will give you reasonable notice of material changes (by email or in the app). If you keep using Offset after the change takes effect you accept the updated terms; if you do not agree, you may cancel before then.

15. General

15.1 Entire agreement. These terms (with the Privacy Policy and any Enterprise agreement) are the whole agreement between us about the service.

15.2 If a provision is unenforceable, the rest still applies. Failing to enforce a right is not a waiver of it. You may not transfer your rights under these terms without our consent; we may transfer ours as part of a sale of the business.

15.3 Governing law. These terms and any dispute about them are governed by the law of Scotland, and the courts of Scotland have exclusive jurisdiction — except that if you are a consumer you may also bring proceedings in the courts of the part of the UK where you live.

15.4 Complaints and disputes. If something goes wrong, please contact us first at support@offsetapp.co.uk so we can try to put it right. If we can't resolve it informally within 30 days, either of us may take it to the courts set out in 15.3. Nothing in this clause stops either of us seeking urgent relief from a court.

15.5 Notices. We will send notices to the email address on your account, or show them in the app. You can send notices to us at support@offsetapp.co.uk or by post to the address in 1.2. An email is treated as received on the next working day after it is sent.

16. Contact

Questions about these terms: support@offsetapp.co.uk.

---

Appendix: Model cancellation form (consumers only)

Complete and return this form only if you are a consumer and wish to cancel your subscription within the 14-day cancellation period (section 4.5). You don't have to use this form: any clear statement will do.

To: Murdo McDermid, trading as Offset App, Tribe Porty, 19 Windsor Place, Edinburgh, EH15 2AJ. Email: support@offsetapp.co.uk

I/We [] hereby give notice that I/We [] cancel my/our [*] contract for the supply of the following service: Offset subscription ([Individual / Practice] plan)

Subscribed on:

Account email address:

Name of consumer(s):

Address of consumer(s):

Signature of consumer(s) (only if this form is sent on paper):

Date:

[*] Delete as appropriate.